Hydraulics and heat

   / Hydraulics and heat #1  

roadhunter

Elite Member
Joined
Mar 23, 2014
Messages
2,633
Location
Wyoming
Tractor
JCB 212SU
I have an attachment that is building an incredible amount to heat in the hydraulics when I operate. I don't' exactly understand what causes heat in hydraulic systems so I thought I would throw this out there and see if anyone can shed some light on this subject.

The machine only has 4 hydraulic circuits.

#1 controls the drive wheels. This valve is always open and has an adjustment to control the wheels speed.
#2 and #3 adjust the spacing of the drive wheels and the angle. These only operate when the handle is pulled
#4 operates the arm on the top drive wheel and has a pressure regulator to adjust the down pressure on the cylinder.

According to the manufacturer this requires 8 GPM of flow to operate. The unit has a pressure regulator and a flow divider installed but strangely I can still build over 2,000 PSI if I open the valve on the tractor even at idle. That makes me think the pressure regulator and flow divider is not working as taht should not be possible. Makes me think there is a restriction in the system causing all the back pressure.

I tried operating this with my old famrall with a PTO hydraulic pump. Input pressure was 900 PSI and the oil overheated to 190+ in less than 10 minutes with no load. IT only has about a 4 gallon tank so the heat had nowhere to go.
When I operate it with my JCB wint 900 PSI of input pressure the oil goes to 175+ in about 20 minutes. Keep in mind this has a large reservoir and oil cooler on the motor.

According to the manufacturer, Rabaud, they say this is normal for the Robopel 250. Everyone I have talked to said that building that much heat is not normal, especially when not under a heavy load.

I guess I'm trying to figure out how hydraulic oil builds heat and where I should look to try to pinpoint the problem. Here are some pics of the machine and valve.

unnamed (1).jpg
unnamed.jpg
unnamed (2).jpg

Is the heat normally built in the pump or more likely in things like drive wheels that require constant flow? What about the circuit that has a pressure regulator, can the regulator cause heat buildup?
 
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   / Hydraulics and heat #2  
The machine only has 4 hydraulic circuits.

#1 controls the drive wheels. This valve is always open and has an adjustment to control the wheels speed.
#2 and #3 adjust the spacing of the drive wheels and the angle. These only operate when the handle is pulled
#4 operates the arm on the top drive wheel and has a pressure regulator to adjust the down pressure on the cylinder.



#1: What type of flow control is being used for the wheel speed? Where is the excess flow directed or diverted to? Depending on the flow regulator style this could be causing a heat issue.

#4: Pressure reducing valves are heat generators IF their is flow across them. In this case I presume this is just keeping a load on a cylinder so there would be minimal flow but then the question becomes what is happening to the flow? If this is a fixed displacement pump it has to go somewhere and it will be dumping to tank at some pressure greater than your reduced pressure. This will create a lot of heat.


simple method for finding point of heat generation is to either touch the components during startup if this can be done safely or use an infrared thermometer and look for the hot spot.
 
   / Hydraulics and heat #3  
A relief valve that prematurely opens can cause heat. Is hyd oil cooler clean? Do you know if JCB 212SU is open or closed center hyd's??
 
   / Hydraulics and heat #4  
how hot does it get in an hour
 
   / Hydraulics and heat #5  
Go to the Yesterday's Tractors Forums and get in the JD section. Look in the archives. The subject was discussed there and it had to do with oscillating valves like Jim eluded to.
 
   / Hydraulics and heat
  • Thread Starter
#6  
The machine only has 4 hydraulic circuits.

#1 controls the drive wheels. This valve is always open and has an adjustment to control the wheels speed.
#2 and #3 adjust the spacing of the drive wheels and the angle. These only operate when the handle is pulled
#4 operates the arm on the top drive wheel and has a pressure regulator to adjust the down pressure on the cylinder.



#1: What type of flow control is being used for the wheel speed? Where is the excess flow directed or diverted to? Depending on the flow regulator style this could be causing a heat issue.

#4: Pressure reducing valves are heat generators IF their is flow across them. In this case I presume this is just keeping a load on a cylinder so there would be minimal flow but then the question becomes what is happening to the flow? If this is a fixed displacement pump it has to go somewhere and it will be dumping to tank at some pressure greater than your reduced pressure. This will create a lot of heat.


simple method for finding point of heat generation is to either touch the components during startup if this can be done safely or use an infrared thermometer and look for the hot spot.

I got to looking at the valve. It appears to be supplied with a 3/8 hose and the first circuit (bottom) runs the drive wheels. There is a dial just to the right that adjust the wheel speed. IT appears that the lines to and from the drive wheels are 3/8. This valve is always engaged as the wheels are always spinning. You can hold it in the middle to stop them or hold it in the opposite direction to reverse wheel direction.

The next 2 circuits are just going to adjustment cylinders and have 1/4" lines. Both are in the center position unless engaged.

Then we come to the top circuit. It controls the arm. This has a pressure relief valve tapped into the supply line with a T. The T and lines are 1/4". This valve is always engaged.

According to my thermometer the heat is coming from the top pressure regulator. It appears to me that all the supply lines on the machine are 3/8", the first valve that receives flow for the wheels is 3/8", but when you come to the top valve the Tee is only 1/4" and the line to the cylinder and to the regulator is only 1/4". So is appears to me that the system is all 3/8" except for that tee and line to the regulator which are only 1/4". The regulator has a much bigger opening that has been bushed down from 1/2" to 1/4".

Could that be the restriction causing issues in the system? I'm no plumber but it sure seems like that is a restriction. Once that oil leaves the regulator there is no backpressure so there is a huge pressure drop. It has to go through the regulator because the valve is always engaged.

IMG_0147.jpg
unnamed (2).jpg
 
   / Hydraulics and heat
  • Thread Starter
#7  
how hot does it get in an hour

It gets up to that 175 temp and stays there. It all depends on how much I open the valve on the tractor. I can build over 2,000 psi of input pressure even idling the tractor and that builds much more heat in the system. I've been trying to keep the tractor valve adjusted where the input pressure is below 1,000 PSI. I have a gauge on the line where I monitor pressure. The manufacturer says that there is a 900 PSI pressure relief valve and a flow divider on the peelers hydraulic system that will prevent excess backpressure but I don't' think it is working correctly as I should not be able to build that much pressure if the relief and flow divider were working correctly.
 
   / Hydraulics and heat
  • Thread Starter
#8  
A relief valve that prematurely opens can cause heat. Is hyd oil cooler clean? Do you know if JCB 212SU is open or closed center hyd's??

Hyd cooler is clean. Oil is clean. I believe it is an open system.
 
   / Hydraulics and heat #9  
I have an attachment that is building an incredible amount to heat in the hydraulics when I operate.

According to the manufacturer this requires 8 GPM of flow to operate. The unit has a pressure regulator and a flow divider installed but strangely I can still build over 2,000 PSI if I open the valve on the tractor even at idle. That makes me think the pressure regulator and flow divider is not working as that should not be possible. Makes me think there is a restriction in the system causing all the back pressure.

I guess I'm trying to figure out how hydraulic oil builds heat and where I should look to try to pinpoint the problem. Here are some pics of the machine and valve.

View attachment 446107

A 'nominal' 1/4" fitting (male) has <45% the cross-sectional area (thus, presumably, flow capacity) of similar 3/8" pieces. In an open center system continuous flow to/thru' any/all circuits must contend with any restriction in each. (8 gpm :eek:)

If the gauge is upstream of the pressure regulator it would show the pump output trying to maintain downstream pressure (to the reg) beyond the 1/4" bits, esp when nothing (cyl, motor) is activated and circuit back-pressure at its lowest.

Anyway, IMO the 1/4" parts should go before you can find any other possible problems. tog
 
   / Hydraulics and heat #10  
For what it's worth, I think you're looking in the wrong direction. By it's very nature, a machine such as this WILL generate heat. You say the machine requires 8 GPM, and has a 900 psi relief valve. It seems to me the input and system operating pressure should then never need to exceed that 900 psi. What does the manufacturer recommend as a practical operating pressure? I would think maybe 700 to 800 max. You have thus far made no mention of how/if you're determining how much flow(GPM) you're trying to push through this thing. Only that controlling the tractor valve can raise the pressure as high as 2000 psi. To me that means the flow is simply too great, and excessive heat is unavoidable.
As for the size of fittings and hoses, to me they seem large enough for the suggested rate of flow.
 
 
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