Hi,
I am pretty new to the Hydraulics and do have a few questions.

I am working on a project which involves a pressure-compensated piston pump. It has a case drain outlet. I was just wondering the need for the case drain outlet? Is it there to drain off the oil that is used to lubricate the pump components?

What type of hoses would be suitable for the case drain? Would a 100R1AT parker hoses be suitable or should a 100R2AT parker hoses should be used?

The pump has also a load sense port. Generally, Would a 100R1AT parker hoses be suitable or should a 100R2AT parker hoses should be used for the load sense?

The maximum pressure of the system is less than 3000 PSI.

I do have one more question. Generally there is a baffle in a reservoir. Should the return line and the case drain line be on the same side of the baffle and the Suction line on the opposite side?

Thanks in advance

quote:

I am working on a project which involves a pressure-compensated piston pump. It has a case drain outlet. I was just wondering the need for the case drain outlet? Is it there to drain off the oil that is used to lubricate the pump components?

The Case Drain handles oil that bypasses any component in the pump that has operating clearances and te small amount of flow that lubricates and lifts the piston shoes off the Swash Plate. On a new pump it runs 4-6% of rated pump flow and the pump shoud be rebuilt or replaced when Case Flow excedes 10% of maximum pump rated flow.

What type of hoses would be suitable for the case drain? Would a 100R1AT parker hoses be suitable or should a 100R2AT parker hoses should be used?

The hose should be equal to the Case Drain Port size or larger and return to tank below the oil level. Pressure in this line should never excede 25-35 PSI since the pump Shaft Seal can give out above 35-40 PSI. Where the line terminates is not important since the flow is low and even though it pure heat energy it is not enough to over heat a system with a nominal sized tank.

The pump has also a load sense port. Generally, Would a 100R1AT parker hoses be suitable or should a 100R2AT parker hoses should be used for the load sense?

I'm not up to Hose Designations. The line will see full pump pressure so it must be capable of operating at that pressure.

The maximum pressure of the system is less than 3000 PSI.

I do have one more question. Generally there is a baffle in a reservoir. Should the return line and the case drain line be on the same side of the baffle and the Suction line on the opposite side?

Take a look at Chapter 6 Fig. 6-5 to see the standard layout and Line connections of a typical hydraulic tank. You can see it in the Basic Ebook at that web site.
http://www.hydraulicspneumatics.com/200/eBooks/

Thanks a lot. Your reply was very very useful. As for my last question on the routing of the case drain line into the reservoir, i did look up at the reference that you had given me, there was no case drain circuit line. But i do strongly believe that it should be on the same side of the baffle as the return line, as

1) Pressure relatively the same as the return line
2) It has some form of heat that needs to be dissipated before the hydraulic oil goes to the suction side.

I do have another question though,

What exactly is the difference between a load sensing system and a constant flow system. For example, I was reading an artical on the following website,

http://www.insidersecretstohydraulics.com/hydraulic-load-sensing.html

They had stated an example of the winch to demonstrate a load sensing system. What difference would it have made, if for that particular case a constant flow system had been used?

Thanks in advance

quote:

They had stated an example of the winch to demonstrate a load sensing system. What difference would it have made, if for that particular case a constant flow system had been used?

I prefer terms like Fixed Displacement Pump instead of (Constant Flow Pump).

A Load Sensing Pump is a Pressure Compensated Pump with an added control that only allows pressure in the circuit to go to 150-250 PSI (Adjustable at the Load Sense Control) as the highest Load Pressure that is fed back to the Load Sense Port through Shuttle Valves.

That means the pump only has flow when an actuator is moving and only 150-250 PSI higher than the highest operating load. So, when the circuit is idle the pump is compensated to no flow at the Load Sense pressure control setting instead of the Compensator setting. And, anytime a load is moving Flow is whatever is required and Pressure is only 150-250 PSI higher than the load until reaching Compensator setting.

It is easy to see that energy input is much less than a Pressure Compensated only pump so heat generation and wear and tear on the system is greatly reduced.

A Fixed Displacement pump operates at full flow continuously and when used to do work at partial flow the excess flow must go across a Relief Valve at Maximum System Pressure and produce a lot of Wasted Energy kmoown as HEAT.

There are Fixed Volume Pumps that use Load Sensing to reduce the Wasted Energy and can be a big Energy Saver for some circuits. I have never used one but have seen them on some Mobile Equipment circuits. They sense system pressure and set the Relief valve slightly higher than the load requires.

Of course the latest Load Sensing system is using a Fixed Volume Pump and a Variable Frequency Drive Motor so the pump only turns when flow is required and only turns fast enough to move an actuator at the desired speed. That means pressure will always be Whatever it Takes to overcome the present load and flow line losses or nothing when no actuators are moving. However, they can be used to maintain a constant holding pressure by turning the pump just fast ebough to maintain the required pressure by overcoming bypass system flow.

These circuits are super efficient, can have pump life far exceeding any system using a standard 1200 or 1800 RPM Motor, don't require a Heat Exchanger and can give almost Servo type speed control.

Does anybody see the need for TRAINED/DEDICATED FLUID POWER Persons who only work on Fluid Power circuits?????????

quote:

Originally posted by Bud T:
Does anybody see the need for TRAINED/DEDICATED FLUID POWER Persons who only work on Fluid Power circuits?????????

No, that's what you're for, Bud! LOL. Anyways, to answer your question about R1 or R2 lines, in this case it depends on the size of the hose. I'll wager you can use R1 lines, because they won't be any bigger than 3/8" and should be able to handle over 3000 psi anyway.

i would plumb the case drain line to the same side of the baffle as the system return. This way, if a pump fails, the case drains can carry large amounts of newly created foriegn material into the tank and there will be less debris to be "ingested" into the system.

quote:

Of course the latest Load Sensing system is using a Fixed Volume Pump and a Variable Frequency Drive Motor so the pump only turns when flow is required and only turns fast enough to move an actuator at the desired speed. That means pressure will always be Whatever it Takes to overcome the present load and flow line losses or nothing when no actuators are moving. However, they can be used to maintain a constant holding pressure by turning the pump just fast ebough to maintain the required pressure by overcoming bypass system flow.

These circuits are super efficient, can have pump life far exceeding any system using a standard 1200 or 1800 RPM Motor, don't require a Heat Exchanger and can give almost Servo type speed control.

Who is doing this (MFG?) i would like to look into it a little bit more.Sounds interesting Thanks

As far as I know any company that had a Pressure Compensated pump now has a Load Sensing option for it.

The load sensing is a secondary control spring that looks at the Pressure required by a load and makes the pump compensator think that it is set 150-200 PSI higher than that load. However when the pressure required to overcome the load reaches compensator setting it takes over and reduces flow to nothing and holds set pressure.

The reason it is so efficient is the pressure required to do the work is only 150-200 PSI higher than required so the pressure drop is low for any given load. Low Pressure Drop equals Low Heat Generation.

A Google search for "Hydraulic Pump+Load Sensing" brought up this pamphlet by Eaton,
http://hydraulics.eaton.com/products/pdfs/03-206.pdf

Plus a lot of others.

There is even Load Sensing for Fixed Volume Pumps that saves sending oil across a Relief Valve at Max System Pressure. A Google search will probably show that circuit also.

And another control that is big in the Mobile Industry is "Horsepower Limiting" that automatically reduces a Pressure Compensated pumps flow to an amount that an engine can handle when pressure increases and tries to take more HP than the engine can handle and still move the machine.

I used the HP Limiting setup on a 25 GPM pump at 2,000 PSI that needed to move a lot of oil at low pressure to get a cylinder in place and then go to Clamp Force. The pump was powered by a 5 HP Electric Motor and had no problems keeping up.

VFDs and water pumps have been used in industry for a number of years-it also has been adapted to hydraulic pumps in other parts of the world. The US not being as "green" is somwhat behind the times.
Maytag
BTW, Ed, if you are listening, how is the new job?

Good one Maytag. I hadn't thought of Variable Frequency Drives as Load Sensing but they are probably the most efficient of all the Load Sensing setups so far. Very little Wasted Energy when coupled with a Vane or Piston pump.

True Load sense systems need to respond to flow demand very quickly. Of course I am assuming you want to have a responsive system/machine. A VFD will not be able to respond to the quick enough to a valve opening demand flow(load sense signal). Pump upstroke time for a load sense system is about 100-200 ms. VFD’s cant do that. Plus you would have to have very solicited controls and sensors.

Also, Please keep in mind.. Piston pumps (the most common Load sense and pressure comp pumps) are designed to operate at particular speeds (mostly 1800rpm) for a number of reasons. I could go into more detail but I won’t labor the issue. Point is.. You do not want the piston pump operating at lower speeds say 0-500rpm. Which the VFD would have to operate to meet min flow demand (0gpm).

VFD’s are great but the load sense system design in genius thousand of applications. I know that they have been around for decades but I see them as the next big wave to replace large industrial fixed displacement systems.

Jerimiah, here is one company that offers VFD pump systems with some fast response claims for performance. They don't give numbers to their response time statements so that would have to be known to fully evaluate their claims.

http://www.kadantunigy.com/#TSAccordionHead737115
Plus an article in H&P Magazine:
http://www.hydraulicspneumatics.com/200/Issue/Article/False/78384/Issue

However, I don't believe anyone claims Servo or even Proportional valve control speeds for the VFD systems. But, they are great pumping systems for saving energy on many present day applications in industry.

ops, another interesting topic

case drain- very important, always follow whatever maximum inside diameter you can have, short as possible, avoid hose if possible ,follow manufacturer instruction with respect to pump mounting style. most often there is at least 2 case drain ports, use the one that is on the upmost when the pump is mounted always, then a nearest portion of the tube or fitting to the case drain must be slightly higher than the highest point of the pump body.

suction line- should always be alone in one side of the baffle plate

use tubes in most cases if possible, hoses are only for flexibility and shock, make it as short as possible.

if you have money use a variable displacement pump(especially piston) with at least a solenoid destroking option. if your actuator is motor always use at least with a load sense.

when i first started with hydraulics, it was with vickers, but the promotion of variable piston was not so great. "if ever you really want to feel the greatness of hydraulic pumps go for the variable piston pumps (whether for open or close loop applications"

i am not updated with new hydraulic system components and applications, but try reading or researching about "HYDRAULIC CONTROL OF THE SECONDARY UNITS". That was the latest application that i read "10 years ago!"

control of piston pump flow using proportional or servo valves has been there decades ago!!!

servo valves also controls the variable displacement motors in control of the secondary unit applications!!!