INDUSTRIAL FLUID POWER EBOOK
Industrial fluid power. Front Cover. Charles S. Hedges, Robert C. Womack, Womack Educational Publications. Womack Educational Publications, startup and run well at temperature. Most industrial hydraulic oils run in the to VI range and are satisfactory for most applications. Fluid Power eBook. Basic laws of fluids, fluid properties and vacuum, plumbing, symbols and typical fluid power systems set the stage for the study of components, symbols and.
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Similar Free eBooks Industrial Power Engineering and Applications Handbook Fluid Mechanics for Civil Engineers - Department of Civil Engineering. Industrial Fluid Power, Vol. 1: Basic Text on Hydraulics, Air & Vacuum for Industrial and Mobile Applications [Charles S. Hedges, Robert C. Womack] on. Read "Industrial Hydraulic Systems: Theory and Practice" by Joji Parambath available from Rakuten Kobo. Sign up today and get $5 off your first purchase.
No consideration for compressibility is necessary in most hydraulic circuits because oil can only be compressed a very small amount. Normally, liquids are considered to be incompressible, but almost all hydraulic systems have some air trapped in them. The air bubbles are so small even persons with good eyesight cannot see them, but these bubbles allow for compressibility of approximately 0.
Applications where this small amount of compressibility does have an adverse effect include: In this book, when presenting circuits where compressibility is a factor, it will be pointed out along with ways to reduce or allow for it. Another situation that makes it appear there is more compressibility than stated previously is if pipes, hoses, and cylinder tubes expand when pressurized. This requires more fluid volume to build pressure and perform the desired work. In addition, when cylinders push against a load, the machine members resisting this force may stretch, again making it necessary for more fluid to enter the cylinder before the cycle can finish.
As anyone knows, gasses are very compressible. Some applications use this feature. In most fluid power circuits, compressibility is not advantageous; in many, it is a disadvantage. This means it is best to eliminate any trapped air in a hydraulic circuit to allow faster cycle times and to make the system more rigid.
Boyle's Law Boyle's Law for gasses states: I t i s the pr i nci ple that, for r elati vely low pr essur es, the absolute pr essur e of an i deal gas kept at constant temper atur e var i es i nver sely wi th the volume of the gas. In down-home language this means if a ten cubic foot volume of atmospheric air is squeezed into a one cubic foot container, pressure increases ten times. Notice that pressure is stated as psia. Normally, pressure gauges read in psi with no additional letter.
Commonly called gauge pressure, psi disregards the earth's atmospheric pressure of The a on the end of psia stands for absolute, and would be shown on a gauge with a pointer that never goes to zero unless it is measuring vacuum. Another type of gauge that shows both negative and positive pressures would have a pointer with an inches-of-mercury in. Hg scale below zero and a psig scale above zero. Both of these gauges could read pressure or vacuum. They are always found in a refrigeration repairperson's tool kit.
Refrigeration units have both vacuum and pressure in different sections of the system at the same time. Figure 1- 5 pictures a typical psig gauge and one type of psia gauge. In the example above, when ten cubic feet of air was squeezed into a one cubic-foot space, both pressures were given in psia. To see what gauge pressure psig would be, subtract one atmosphere from the psia reading. To calculate the amount of compression of air in a system, always use absolute pressure, or psia, not psig.
To what will pressure increase when an external force pushes the piston back until the space behind the piston is two cubic foot? It is obvious the pressure will rise four times. For the correct answer, gauge pressure must be changed to absolute pressure.
In this case by adding one atmosphere to the psig reading. Now multiply the Finally, to return to gauge pressure, subtract one atmosphere from the absolute pressure.
Notice that the correct pressure is Temperature was not considered in both preceding cases, but notice that the law says kept at constant temperature. Compressing a gas always increases its temperature because the heat in the larger volume is now packed into a smaller space.
The next law says that increasing temperature increases pressure if the gas cannot expand. This means the pressures given are measured after the gas temperature returns to what it was originally. Gauges today read in psi and bar.
Bar is a metric or SI unit for pressure and is equal to approximately the barometer reading or one atmosphere. One atmosphere is actually Charles' Law Heating a gas or liquid causes it to expand.
Continuing to heat a liquid will result in it changing to the gaseous state and perhaps spontaneous combustion. If the gas or liquid cannot expand because it is confined, pressure in the contained area increases. This is stated in Charles' Law as: The volume of a fixed mass of gas varies directly with absolute temperature, provided the pressure remains constant.
Because fluid power systems have some areas in which fluid is trapped, it is possible that heating this confined fluid could result in part damage or an explosion. If a circuit must operate in a hot atmosphere, provide over pressure protection such as a relief valve or a heat- or pressure-sensitive rupture device. Never heat or weld on any fluid power components without proper preparation of the unit.
Static head pressure The weight of a fluid in a container exerts pressure on the containing vessel's sides and bottom.
This is called static head pressure. It is caused by earth's gravitational pull. A good example of head pressure is a community water system. Figure shows a water tower with a topmost water level of 80 feet. A cubic inch of water weighs 0. Therefore a one square-inch column of water will exert a force of 0. This works out to. For the water tower in Figure , the pressure at the base would be: This pressure is always available, even when no pumps are running.
Of course, if the water level drops, static head pressure also will drop. The specific gravity of hydraulic oil is approximately 0. Usually this fraction is rounded to 0. If the water tower were filled to 80 ft with oil, it would exert a pressure of 32 psi at ground level. Other fluids would develop a higher or lower static pressure according to their specific gravities.
This pressure is only realized at ground level at the tower. Outlets at other levels would be higher or lower according to their distance below the fluid surface. Tanks seen on most water towers simply store volume. Pressure does not drop rapidly or require frequent pump starts to maintain the fluid level. The size or shape of the tank does not affect pressure at the base. Pressure at the base of a straight ft pipe would be the same, but useful volume before pressure drop would change drastically.
Always remember: Head pressure can have an adverse effect on a hydraulic system because many pumps are installed above the fluid level. This means the pump must first create enough vacuum to raise the fluid and then create even higher vacuum to accelerate and move it. Therefore there is a limit to how far a pump can be located above the oil level. Most pumps specify a maximum suction pressure of 3 psi. At 4- to 5-psi suction pressure, pumps start to cavitate.
At 6- to 7-psi vacuum, cavitation damage is severe and noise levels increase noticeably. The effects of cavitation are covered fully in Chapter 8, Fluid power pumps and accessory items. Axial- or in-line- piston pumps are especially vulnerable to high inlet vacuum damage and should be set up below the fluid level to produce a positive head pressure.
Many modern hydraulic systems place the pump next to the reservoir so the fluid level is always above the pump inlet. With this type of installation the pump always has oil at startup and has a positive head pressure at its inlet.
Everything possible should be done to keep pressure drop low in the pump inlet line because the highest possible pressure drop allowable is one atmosphere The earth's atmosphere the air we breathe exerts a force of This pressure covers the whole earth's surface, but at elevations higher than sea level, it is reduced by approximately 0. This pressure of earth's atmosphere is the source of the power of vacuum.
The highest possible vacuum reading at any location is the weight of the air above it at that time. A reading of maximum vacuum available is given during the local weather forecast as the barometer reading. Divide the barometer reading by two to get the approximate atmospheric pressure in psi. This force could be directly measured if it were possible to isolate a one square-inch column of air one atmosphere tall at a sea level location. Because this is not possible, the method used to measure vacuum is demonstrated in Figure Submerge a clear tube with one closed end in a container of mercury and allow it to fill completely.
The tube must be more than in. After the mercury displaces all the air in the tube, carefully raise the tube's closed end, keeping the open end submerged so the mercury can't run out and be replaced by air. When the tube is positioned vertically, the liquid mercury level will lower to give the atmospheric pressure reading in inches of mercury H g at sea level.
The mercury level will fluctuate from this point as high and low-pressure weather systems move past. If the tube had been in. The reason the mercury does not all flow out is that atmospheric pressure holds it in.
This barometer could have been built using another liquid but the tube would have to be longer because most other liquids have a much lower specific gravity than mercury's Water, with a specific gravity of 1. Vacuum pumps can be similar in design to air compressors. There are reciprocating-piston, diaphragm, rotary-screw, and lobed-rotor designs. See air compressor types in Chapter 8, Fluid power pumps and accessory items.
Imagine hooking the inlet of an air compressor to a receiver tank and leaving the outlet open to atmosphere. As the pump runs, it evacuates air from the receiver and causes a negative pressure in it. Vacuum pumps are an added expense and normally are only found in facilities that use a constant supply of negative pressure to operate machines or make products. Vacuum generators that use plant compressed air as a power source are also available. These components have no moving parts but use plant air flowing through a venturi to produce a small supply of negative pressure.
Figure shows a simplified cutaway view of a venturi- type vacuum generator. The device consists of body A with compressed-air inlet B that passes air flow through venturi nozzle C.
The air exhausts at a higher velocity to atmosphere through orifice D. As air at increasing velocity flows past opening E near the venturi nozzle, it creates a negative pressure and draws in atmospheric air through port F. Port F can connect to any external device that needs a vacuum source.
A vacuum gauge at port F shows negative pressure when compressed air is supplied to port B. Vacuum generators are inexpensive, but can be costly to operate. For every 4 cfm of air supply required to power them, they use approximately one compressor horsepower. For this reason, venturi-type vacuum generators usually are installed with a control valve to turn them on only when needed. As a result, vacuum is not powerful enough to do much work unless it acts on a large area.
Many industrial vacuum applications have to do with handling parts. Large-area suction cups can lift a large heavy part with ease, as illustrated in Figure When the lift rises, negative pressure vacuum inside the suction cups causes atmospheric pressure on the opposite side of the part to push it up.
Industries such as glass and wood manufacturing use vacuum to hold work pieces during machining or other operations, as shown in Figure A resilient seal laid in a groove in the fixture keeps atmospheric air from entering the cavity beneath the part.
This groove can be cut to match the contour of the part. In machining operations, the seals can isolate interior cutouts, allowing them to be removed while firmly holding the rest of the piece. Heated plastic sheet can be vacuum-formed to make some products at a much lower cost than other types of plastic forming, as suggested in Figure Forming heated plastic sheet in a cavity or over a shape is quick and positive. When atmospheric pressure tries to fill the negative-pressure area under the softened sheet, the sheet is forced into the desired shape.
Large parts such as pickup-truck bed liners are formed by this method. Quiz Chapter 2: Hydraulic Fluids For long service life, safety reasons, and reliable operation of hydraulic circuits, it is very important to use the correct fluid for the application. The most common fluid is based on mineral oil, but some systems require fire resistance because of their proximity to a heat source or other fire hazard. Water is also making its return to some hydraulic systems because it is inexpensive, fireproof, and does not harm the environment.
Transmit energy. The main purpose of the fluid in any system is to transmit energy. Electric, internal combustion, steam powered, or other prime movers drive a pump that sends oil through lines to valves that control actuators. The fluid in these lines must transmit the prime movers energy to the actuator so it can perform work.
The fluid must flow easily to reduce power losses and make the circuit respond quickly. In most hydraulic systems, the fluid must have good lubrication qualities. Pumps, motors, and cylinders need ample lubrication to make them efficient and extend their service life.
Mineral oils with anti-wear additives work well and are available from most suppliers. Some fluids may need special considerations in component design to overcome their lack of lubricity.
Fluid thickness can be important also because one of its requirements is for sealing. Almost all pumps and many valves have metal to metal sealing fits that have minimal clearance but can leak at elevated pressures. Thin watery fluid can flow through these clearances, reducing efficiency and eroding the mating surfaces. Thicker fluids keep leakage to a minimum and efficiency high. There are several areas that apply to specifying fluids for a hydraulic circuit.
Viscosity is the measure of the fluids thickness. It is a measuring system set up by a man named Saybolt. Simply stated, the system takes a sample of fluid, heats it to F, and them measures how much fluid passes through a specific orifice in a certain number of seconds.
Viscosity is most important as it applies to pumps. Most manufacturers specify viscosity limits for their pumps and it is best to stay within the limits they suggest. The prime reason for specifying a maximum viscosity is that pressure drop in the pump suction line typically is low and if the oil is too thick, the pump will be damaged due to cavitation.
A pump can move fluid of any viscosity if the inlet is amply supplied. On the other end, if fluids are too thin, pump bypass wastes energy and generates extra heat.
All other components in the circuit could operate on any viscosity fluid because they only use what is fed to them. However, thicker fluids waste energy because they are hard to move. Thin fluids waste energy because they allow too much bypass.
Viscosity index or VI is a measure of viscosity change from one temperature to another. It is common knowledge that heating any oil makes it thinner. A normal industrial hydraulic circuit runs at temperatures between and F. Cold starts could be as low as 40 to 50 F. Using an oil with a low VI number might start well but wind up with excessive leakage and wear or cause cavitation damage at startup and run well at temperature.
Most industrial hydraulic oils run in the to VI range and are satisfactory for most applications. It should be at least lower than the lowest temperature to which the system will be exposed so the pump can always have some lubrication.
Consider installing a reservoir heater and a circulation loop on circuits that start or operate below 60 F. Refined mineral oil does not have enough lubricating qualities to meet the needs of modern day hydraulic systems. Several lubricity additives to enhance that property are added to mineral oil as a specific manufacturers package.
These additives are formulated to work together and should not be mixed with others additives because some components may be incompatible. Refined mineral oil also is very much affected by temperature change. In its raw state it not only has low lubricity but also would thin out noticeably with only a small increase in temperature.
Viscosity modifiers enhance the oils ability to remain at a workable viscosity through a broad temperature range. There are several causes of hydraulic oil oxidation.
These include contamination, air, and heat. The interaction of these outside influences cause sludge and acids to form.
Oxidation inhibitors slow or stop the fluids degradation and allow it to perform as intended. Wear inhibitors are additives that bond with metal parts inside a hydraulic system and leave a thin film that reduces metal-to-metal contact. When these additives are working, they extend part life by reducing wear. In most hydraulic systems, fast and turbulent fluid flow can lead to foaming.
Anti-foaming agents make the fluid less likely to form bubbles and allow those that do form to dissipate more rapidly. Moisture in the air can condense in a hydraulic reservoir and mix with the fluid. Rust inhibitors negate the effect of this unwanted water and protect the surfaces of the systems metal components. All of these additives are necessary to extend system life and improve reliability. Overheating the fluid can counteract the additives and decrease system efficiency.
Overheating also thins the oil and reduces efficiency because of internal bypassing. Clearances in pump and valve spools let fluid pass as pressure increases, causing more heating until the fluid breaks down.
External leaks through fittings and seals also increase as fluid temperatures rise. Another problem caused by overheating is a breakdown of some seal materials.
Most rubber compounds are cured by controlled heat over a specific period of time. Continued heating inside the hydraulic system over long periods keeps the curing process going until the seals lose their resiliency and their ability to seal. It is best if hydraulic oil never exceeds F for any extended period. Installing heat exchangers is the most common cure for overheating but designing heat out of a circuit is the better way. Cold oil is not a problem as far as the oil is concerned but cooling does increase viscosity.
When viscosity gets too high, it can cause a pump to cavitate and damage itself internally. Thermostatically controlled reservoir heaters easily eliminate this problem in most cases. Fire-resistant fluids Certain applications must operate near a heat source with elevated temperatures or even open flames or electrical heating units.
Mineral oil is very flammable. It not only catches fire easily but will continue to burn even after removing the heat source. This fire hazard situation can be eliminated by several different choices of fluids. These fluids are not fireproof, only fire-resistant, which means they will burn if heated past a certain temperature but they will not continue to burn after removing them from the heat source.
Generally, the fire-resistant fluids do not have the same specifications as mineral oil-based fluids. Pumps often must be down rated because the fluids lubricity or specific gravity is different and would shorten the pumps service life drastically at elevated pressures or high rotary speeds.
Some fire-resistant fluids are not compatible with standard seal materials so seals must be changed. Always check with the pump manufacturer and fluid supplier before using or changing to a fire-resistant fluid. Water Originally, hydraulic circuits used water to transmit energy hence the word hydraulics. The main problem with water-filled circuits was either low-pressure operation or very expensive pumps and valves to operate with this low viscosity fluid above to psi.
When huge oil deposits were discovered, mineral oil replaced water because of its additional benefits.
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Water made a brief comeback during an oil shortage crisis but quickly succumbed when oil flowed freely again. In the late 90s, water again made inroads into oil-hydraulic systems.
Several companies have developed reliable pumps and valves for water that operate at to psi. There are still limitations such as freezing to using water, but in certain applications it has many benefits. One big advantage is that there are fewer environmental problems during operation or in disposing of the fluid. Price also is a factor because water costs so little and is readily available almost anywhere. Some suppliers are making equipment that operates on seawater to eliminate possible contamination of the earths potable water sources.
These systems operate at elevated pressures without performance loss. This type of fluid is known as high water- content fluid or HWCF. This mixture takes care of most of the lubricity problems but does not address low viscosity concerns.
Therefore, systems using HWCF still need expensive pumps and valves to make them efficient and extend their life. Rolling mills and other applications with molten metals are one area where HWCF is prevalent. Often the soluble oil is the same compound used for coolant in the metal-rolling process. This eliminates concerns about cross-contamination of fluids and the problems it can cause.
Again, these are not common fluids because they require special oil and continuous maintenance to keep them mixed well and their ratio within limits. Most manufacturers do not want the problems associated with water-in-oil emulsions so their use is very limited.
Water glycol A very common fire-resistant fluid is water glycol. This fluid uses water for fire resistance and a product like ethylene glycol permanent anti-freeze for lubricity, along with thickeners to enhance viscosity. Ethylene glycol will burn, but the energy it takes to vaporize the water present quickly quells the fire once it leaves the heat source.
This means a fire would not spread to other parts of the plant. Always remember fire-resistant not fireproof. Water glycol fluids are heavier than mineral oil and do not have its lubricating qualities, so most pump manufacturers specify reduced rpm and lower operating pressures for water glycol.
In addition, the water in this fluid can evaporate, especially at elevated temperatures, so it must be tested regularly for the correct mixture. Cost is also a consideration. Water glycol is more expensive than oil and requires most of the same considerations when disposing of it. Always check with the pump manufacturer before specifying water glycol fluid to see what changes are necessary to run the pump with this fluid. Seal compatibility is usually not a problem, but always check each manufacturers specifications before implementing this fluid.
In addition, it is imperative to completely flush a system of any other fluids before refilling with water glycol. Synthetics The other main fire-resistant fluids are synthetic types.
They are made from mineral oil, but have been processed and contain additives to obtain a much higher flash point. It takes more heat to start them burning but there is not enough volatile materials in them to sustain burning. These fluids may catch fire from a pot of hot metal but quickly self-extinguish after leaving the heat source.
Synthetic fluids retain most of the qualities of the mineral oil from which they are derived, so most hydraulic components specify no operating restrictions. However, most of these fluids are not compatible with common seal materials so seal specification changes are usually necessary.
Special consideration must be given to handling of synthetics because they can cause skin irritation and other health hazards. Also most synthetic fluids require protective epoxy paint for all components in contact with them. Of all the fluids discussed, synthetics are the most expensive. They can cost up to five times more than mineral oil.
No matter which fluid is chosen, design the circuit to work in a reasonable temperature range; install good filters and maintain them; and check the fluids regularly to see if they are within specification limits. A good operating temperature range is between 70 and F with the optimum being around F. A rule of thumb would be: Overheating hydraulic fluids is second only to contamination when it comes to reasons for fluid failure.
Continuous filtration of any hydraulic system is necessary for long component life. Fluids seldom wear out but they can become so contaminated that the parts they drive can fail. The filter section of this book offers some good recommendations on keeping fluid clean. Even with the best of care, any hydraulic fluid should be checked at least twice a year. Systems located in dirty atmospheres may need to be checked more often to see if a pattern exists that requires special consideration.
Pay close attention to the sampling process and packaging procedures recommended by the test facility that will process the sample.
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Expect a report on the level of contamination plus an analysis of the additive contents, water content, ferrous and non-ferrous material amounts, and any other problem areas the test facility finds. Use this information to know when to change fluids and to check for abnormal part wear problems. New oil or other fluids from the supplier are not necessarily clean.
The fluids are shipped in drums or by bulk, and there is no way of knowing how clean these Fluid Power eBook Fluid Power Basics http: Filter cart used to transfer hydraulic fluids and its circuit schematic diagram Fig. Some suppliers offer filtered oil with a guaranteed contamination level at added cost.
Otherwise, about the lowest level of contamination from most manufacturers is 25 microns. Anytime a system needs new fluid, it is best to use a transfer unit, Figure , with a micron or finer filter in the loop. Another way of filtering new or refill fluid is with a filter permanently attached to the reservoir, Figure In this arrangement, the breather or other possible fill points should be made inaccessible.
The filter cart shown in Figure can also be used to filter any hydraulic unit in the plant. Instead of this filter unit sitting idle except when filling systems, set it up at a machines power unit for a timed run. Place the suction hose in one end of the reservoir and the return hose in the opposite end. This adds a continual filtration loop to any machine even when the machines main pump is shut off. Run the cart until the fluid is clean and then move is to another power unit. Repeating this process on a regular schedule can assist the hydraulic units filters and add extra life to the fluid and the hydraulic components.
This process may also show a pattern on machines that have a contamination problem. Hydraulic fluids should be stored in a clean dry atmosphere. Keep all containers closed tightly and reinstall covers on any partially used drums. Never mix fluids in any hydraulic system. Make sure all containers are clearly marked and segregated so fluids will not be mixed with one another. Mixing fluids can result in damage to components and some combinations are very difficult to clean up.
Be especially careful when mineral oils and synthetic or water-glycol fluids are used in different parts of the same plant. Fluids are the lifeblood of any hydraulic system and should be given the utmost care. Quiz Chapter 3: Plumbing Poor plumbing practices can permanently cripple a fluid power circuit even if it was designed with the best engineering practices and assembled with the most up-to-date components. Undersized lines, elbows instead of bends, incorrect component placement, and long piping runs are a few of the items that strangle fluid flow.
Other problems, such as using tapered pipe threads or lines with thin walls, can make a circuit a maintenance nightmare that requires daily attention. Fortunately, there are numerous publications that assist in specifying correct line size and conductor thickness to give low pressure drop and safe working-pressure limits. Because pneumatic circuits are less complicated and operate at lower pressures, they are not as vulnerable to plumbing problems.
One very important aspect that often is overlooked is the length and size of lines between the valves and actuators.
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Piping between the valve and actuator should be as short as possible and of the minimum diameter to carry the required flow. The reason for this is that all the air in the pipes between the actuator and valve is wasted every cycle. These runs must be filled to make the device move but the air it takes to fill them does no work. During each cycle, air in the actuator lines exhausts to atmosphere without helping cycle time or force. For this reason, always mount the valve close to the actuator ports.
Another aspect of plumbing a pneumatic system is the in-plant pipe installation procedure. To get the required amount of compressed air to the point of usage requires some planning -- or the site may be starved at times. Pipe size selection chart in feet for plant-air systems Fig. Typical grid system layout for plant air Pipe materials and size: Air systems are normally plumbed with Schedule 40 black iron pipe.
Galvanized pipe is not recommended because some galvanizing material may flake off and get into moving parts. Several other available plumbing materials could be used for air piping because pressure is relatively low.
Some mechanics recommend plastic pipe, but be aware a few synthetic compressor lubricants attack plastic and cause it to lose strength. This type of damage weakens the plastic until it can burst, sending shards of plastic flying everywhere in the plant. Never use any piping material not specifically designated by code. To help select pipe size, the chart in Figure shows flow in cfm down the left-hand side, length of run in feet across the top, and minimum Schedule 40 pipe size in the body at the intersection of these two.
This chart is based on a 1-psi pressure drop for the run lengths given. The right-hand column shows approximate compressor horsepower for the flow figures on the left.
Using larger than specified pipe is of little help in reducing pressure drop, but provides more storage volume to handle short brief-flow needs. This chart does not consider fittings and valves, but they also must be considered when figuring the length of a run. Add 5 to 7 feet of pipe length for each fitting or valve -- to be on the safe side.
Not having enough air to run the equipment is expensive, so never try to save a few cents at installation by skimping on pipe size. One or two pipe sizes over minimum add little to cost up front, but can make a big difference later. It is less expensive to run oversize pipe initially than to have to add a line later.
There are three basic compressed-air piping layouts that meet the requirements of most industrial plants. Some facilities may have two or more of these systems to handle special needs. In general, smaller plants use a modified grid system, especially when the facility is growing. A unit distribution system offers flexibility, but can be expensive up front.
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A loop system is best suited to new construction; it provides extra storage capacity and dual supply for short bursts of high flow.
Figure shows a typical grid-system layout using a centrally located air compressor. All air from the receiver goes to a large header pipe that runs down the center of the plant or department. Typical loop-piping system layout for plant air Fig. Typical unit distribution layout for plant air down to specific machines.
With preplanning for future working drops, this arrangement is very flexible. Figure shows a typical loop piping system for compressed air. Again, the compressor and receiver are at a central location. The oversized loop around the periphery of the plant -- or department -- adds storage and allows flow with low pressure drop.
It also allows for short bursts of high-volume flow to any section because flow in the loop is bi-directional. Another way to get short high-volume flows with any of these piping systems is to install extra receiver tanks at or near areas that need such flow.
Figure illustrates a unit distribution layout that works well in plants that run departments on different days or shifts -- or plants that started out small and added compressors as business grew. It is the most expensive configuration of the three for a new installation, so is not often used there.
One advantage of the multiple compressors is that there is always backup air available for critical operations should a single compressor fail. The disadvantage.
See Figure 2 — Insert Permissible Noise Exposure Hydraulic system leaks and their sources The four primary reasons for leakage in hydraulic systems include poor system design, substandard component quality, improper installation, and abuse. Design — Excessive strain on hydraulic lines, because of a design that fails to allow for expansion and contraction, as well as improper clamping and spacing, may lead to leaks.
It is critical to allow for movement under load. For example, cylinders with non—centerline mountings tend to sway under large loads. Rigid tubing connected to the cylinder end caps will be subject to forces and movement, and may leak. Overhung cylinders require additional support to prevent cylinder movement on the unsupported end. It should be noted that cylinder length changes with pressure and temperature. Quality — Unless quality fittings, tubing and mating ports are used during installation, the hydraulic system may be exposed to potential leaks because of faulty material.
Using quality fittings and ensuring proper installation are the best ways to reduce future maintenance activities.
Installation — Improper tube preparation and assembly may lead to hydraulic system leaks. Prying a poorly bent tube in place strains the joint making it prone to leakage. Improper cutting, flaring, and brazing all lead to potential leakage. Tube overflare interferes with nut ID. Proper brazing the face seal requires that the sleeve be positioned onto the tube with no more that a 0. New technology eliminates the brazing process and its problems.
In place of the brazing procedure, an orbital cold forming process produces a flat, smooth, rigidly supported sealing surface on the tube end. This process is known as flanging. Incorrect torque, alignment, and positioning can affect the assembly of fittings. Burrs, scratches, nicks, foreign particles, pinched o-rings and faulty sealants may also cause leakage.
When troubleshooting fitting failures, determine the location of the leak, then check the joints for proper tightness. If the leak persists, check for correct assembly. It may be necessary to remake the joint.
Abuse Failures — There are multiple ways to abuse hydraulic system components. Common examples are:. Do not remove protective caps and plugs from components until ready to assemble. A leak does not always equal tighten the fitting.
Never use tubing as structural support. Filtration Filtration systems and components present another potential source of hydraulic system leaks. A filter maintenance schedule should be set up and followed diligently. Different filter media and different types of filtration systems present an array of different advantages and disadvantages. This requires an enormous amount of force that you can only achieve using a hydraulic system.
A hydraulic car crushing machine During the processes, this scrap metal baler will compact the car into a small shape that can easily be processed. Depending on the nature of the application, you can choose from large car crushers that use standard hydraulic power unit or a mobile crusher that uses a mini hydraulic power pack. These may include hydraulic cutters, presses, log splitting machines, etc. As I had indicated earlier, hydraulic systems reduce the cost of performing tasks and labor required.
Such shears have mini hydraulic power packs. Another hydraulic cutter that plays and integral during emergencies is the Jaws of Life. It is a popular hydraulic rescue tool you can use rescue accidents victims from the wreckage of the vehicle.
Hydraulic shears The hydraulic rescue tools use either micro or mini hydraulic power units. This gives an accurate and a faster cutting power. With the help of either a standard hydraulic power pack or a mini hydraulic power pack, this machine press can double production rates in most manufacturing processes.
Hydraulic press machine These hydraulic presses are available in different capacities that range from 5 tons to over tons. Therefore, you can choose from small hydraulic presses to large hydraulic presses. Most of these machines can strip and cut electric wires at the same time. A hydraulic cable stripping machine This double function makes them handy and useful in electrical installation. Being a portable machine, the cable strippers mostly come with a mini hydraulic power unit.
With the right machine, one person can comfortably slip firewood for both residential and commercial use. Hydraulic log splitting machine The hydraulic log splitter piston pushes the log into a stationary blade that does the splitting. Alternatively, you may find other designs where the log remains stationary as the blade moves to split the log.
You can opt for an electric or gas log splitter. However, if you need something that is mobile or portable, a gas wood splitter is the best option. Depending on the nature of the task at hand, you may require abrupt braking or smooth and soft braking mechanism. A hydraulic braking system All these require an efficient and a reliable braking mechanism. You can classify them based on the type of the cylinder such as swing action, vertical or threaded body cylinder. A hydraulic clamp and fork lift.
Image source — Direct Industry Also, they have a varying clamping capacity that may range between lbs and 6,lbs.
You can opt for a single acting or double acting hydraulic clamp. Most of these cylinders come with a mini hydraulic power pack. These beds can slowly adjust to the required position. Electric hospital bed These patient beds are common in the intensive care units.
With the help of a hydraulic power pack, doctors can control the position of the bed. It can tilt to different angles. That is, adjust the hospital bed mattress to a position that makes the patient comfortable. This revolutionary technology helps reduce pulmonary complications, ensure safety and achieve the required lateral therapy, among other functions. The hydraulic patient lifts can handle the heavy weight of the patient.On the other hand, its symbol makes all features immediately clear.
Relief Valves and Unloading Valves Why a relief valve? Alternatively, you may also opt for the digital torque wrench. At first look, it may appear that mechanical or hydraulic leverage is capable of saving energy. Pressure is specified in working and burst values similar to pipe. Most manufacturers do not want the problems associated with water-in-oil emulsions so their use is very limited.
Another situation that makes it appear there is more compressibility than stated previously is if pipes, hoses, and cylinder tubes expand when pressurized. This requires more fluid volume to build pressure and perform the desired work.
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