Working Under Pressure - Hydraulic Compressor Drives Save Space and

seem foreign at first but they operate on principles familiar to us all. The engine drives a pump, not unlike a compressor, but it pumps incompress- ible oil.That oil travels through heavy duty,steel- wrapped hoses and various flow controls to do work by moving cylinders or (in our case) turning motors. Having done this work,the Working Under Pressure 3 Hydraulic Compressor Drives Save Space and Cost on HD Equipment Many specialty and off-road vehicles already have hydraulic systems on board, and it is often more efficient to drive the air condi- tioning compressor from the same system.<br><br> An investment in learning to install and repair these systems can add to your bottom line. Would you rather leak-check a pair of twenty foot refrigerant hoses running from the truck engine to the crane cab or work on the self-contained A/C wall unit? T he words chydraulic air conditioning dsend many service companies running.Visions of complexity and unfamiliar controls come to mind.But there is no need to shy away from these systems;there are many fleets of vehi- cles across the country that have or need these sys- tems.A little knowledge in this area can lead you to new customers and expand your business.<br><br> by Bill Kerr,Product Manager,Visionaire Inc. ©MACS2006 oil is now warmer and travels through a heat exchanger and filter before returning to the oil tank. Hydraulic motors have three ports; one in,one out (to the heat exchanger), and the case drain which goes directly back to the oil tank.Various flow dividers can split hydraulic flow from one pump to go to two or more separate circuits.Relief valves act as a safety to prevent excess pressure from building up.Solenoid valves work to control oil flow or switch it between circuits.A large vehicle may have several hydraulic pumps and dozens of circuits.The whole system is designed to stay within the power limits of the engine and not produce so much heat as to overwhelm the heat exchanger and overheat the oil.<br><br> Care is taken whenever an air condi- tioner circuit is added to not upset the hydraulic system 9s balance. Oil flow is measured in gallons per minute,and pressure in PSI or bar.Special training is required to service the hydraulic portion of any machine,and you should leave the hydraulic plumbing to the experts.The oil is often very hot (140- 180°F) and may be under pressures exceeding 3000 p.s.i. Servicing a hydraulic driven com- pressor,or installing one,can be pretty straightforward.The most common type is the hydraulic belt drive.<br><br> Belt-driven systems typically use a Sanden or Seltec heavy duty compressor connected to a hydraulic motor by stan- AC TION " July/August 200619 Working Under Pressure 3 Simple and straightforward, the hydraulic motor is connected to this compressor by the drive belt. Controlling the oil flow allows compressor regulation independent of engine speed. Direct-drive compressors can save space and weight in tight-fit locations.<br><br> Fewer moving parts means extended longevity and reduced maintenance costs. Don 9t let the word chydraulic d scare you away... ©MACS2006 20AC TION " July/August 2006 Working Under Pressure 3 dard automotive belts.The clutch circuit is wired like an engine driven system.Often a valve turns the hydraulic motor on and off with the air conditioner system.<br><br> Never work on the compressor or belts with the vehicle engine running, even if the hydraulic motor seems to be off.If the hydraulic motor is leaking, won 9t turn or is otherwise damaged,have it replaced with a factory-approved one. Many motors look the same but the inter- nal components (gears,bearings,and seal material) can vary dramatically.Use of incorrect parts can sometimes cause dra- matic results! Direct-drive compressors connect the hydraulic motor directly to the shaft of a specially prepared compressor.Since there is no clutch,the compressor must be cycled on and off with a hydraulic control valve.To find the control valve,trace the cclutch dcircuit back from the thermostat.<br><br> These valves generally have a replaceable electromagnetic coil which functions much like a clutch coil. Since there is no clutch to slip,clutch coil,or bearing to ruin the compressor, these compressors tend to be extremely durable.To check for a seized compressor on a direct drive system,it is necessary to separate the coupling between the com- pressor and motor to see which is at fault. A clattering noise inside the coupling housing may indicate a worn cspider, dthe cushion between the metal parts of the coupling.As with other hydraulic compo- nents,it is critical to use factory-approved replacement parts.<br><br> Don 9t let the word chydraulic dscare you away 3 other than the compressor drive,these air conditioners work like any other.Most repairs involve the simple refrigerant leaks,failed switches,worn fans and blowers (not to mention the effects of deferred maintenance) that we commonly see on commercial vehicles. There are some systems on the mar- ket that have hydraulically powered fans and blowers.Due to their complexity and specialized parts they are generally not repaired in the field but are returned to the factory for refurbishment. There is a significant opportunity in aftermarket sales of hydraulic drive sys- tems.They make it possible to cool vehi- cles where it was difficult or impossible before.Often these specialized machines are in fleets,and one successful service call or sale could lead to other opportunities.<br><br> Many cranes,for instance,have no other way to cool the operator since the cab is separated from the engine by a 360° swivel.Forestry,rail maintenance,waste handling,marine,and mining are all fields that make good use of this technology. Self-contained air conditioners have the compressor,condenser,and evaporator all in one package.Since they are already plumbed and charged with refrigerant, they are very straightforward to install. Usually it 9s just a matter of mounting the unit on a cab wall or rooftop and running the appropriate ducting.Equipment fleet owners typically have qualified hydraulic mechanics available,and the final hydraulic connections should be made by the hydraulic technician.<br><br> Where self-contained systems are not appropriate,individual heavy duty air conditioning components can be mixed and matched with hydraulic compressors to create a custom installation.The com- pressor vendor is a good source of infor- mation on appropriate component com- binations. There are good sources of informa- tion available.System manufacturers will supply the range of hydraulic flows and pressures recommended for their compo- nents.Vehicle manufacturers document their machines with hydraulic schematic diagrams and OEM 9s often offer specific guidance on the attachment of accessories such as hydraulic drive compressors.If you become interested in performing the hydraulic work yourself,most hydraulic component suppliers offer training. As you see,hydraulic compressor dri- ves are not that different from the ones we are used to working with every day.With a little patience and study you can open up new markets for your service,and new avenues of profitability.<br><br> I Bill Kerr has been with Visionaire for ten years.He supervises the development of ven- tilation systems for off road equipment OEMs. Founded in 1994 in Grand Prairie,Texas, Visionaire Inc.,focuses on air conditioning, heating,and cab pressurization solutions for heavy duty off road vehicles.They were early innovators in the development of self con- tained hydraulic powered air conditioning systems for rail and oilfield applications. Special vehicles bring special problems.<br><br> This rail ballast vehicle requires a compact and robust air conditioner that will withstand severe vibration and heavy dust. The self contained, roof-mounted A/C unit uses a hydraulic compressor. ©MACS2006<br><br>

less