Hi everyone, I’m experiencing an overheating issue with a closed hydraulic system. The system consists of a Sauer SP23 hydraulic pump and a hydraulic motor, driving a concrete mixer. It operates normally, but it overheats over time. Has anyone encountered a similar issue with a closed hydraulic system? Any advice on possible causes and solutions would be greatly appreciated! Thanks in advance!
What size is the hydraulic reservoir? Does it have a hydraulic cooler? Any hydraulics used continuously will create heat so you need to have a large enough reservoir to help dissipate some of the heat or add an oil cooler. How hot is the oil getting? Hydraulics can be hot to the touch and not overheated.
It blow out hydraulic oil from reservoir, so too hot, it is closed loop system have heat exchanger and reservoir in same place, it works normal but overheating, can it be wrong settings on purge valve on hydraulic motor?
Did it used to work good without overheating? There needs to be extra space for the oil in the reservoir because it will expand when heated. Maybe you can rig up a cooling fan on the heat exchanger. How many gallons does the system hold and did you measure the temperature? It's also possible you're over working the motor. Some pics. of your set up may help to find a solution.
So, in a closed loop system, on the motor, there will be a leakage to tank. That is set with a loop flushing valve. That valves pressure adjustment is spec's by mfr. The purpose of this valve is to let oil out so that fresh oil from tank can enter the circuit and cool it down. I would consult with mfr to get the spec and where the adjustment is on the motor. Having said all that, have you serviced your hydraulics? Changed the filter(s), cleaned coolers, checked for obstructed or kinked hoses? Good luck in your search.
I would suggest following the circuit with a non contact temperature gun or a thermal camera to see what is adding so much heat to the system. Could be a bad bearing, bad pressure relief valve, clogged filters, bad thermal bypass valve, failing motor and numerous other possible faults that would add more heat to the system than can not be disapated fast enough to hold normal operating temps. This would be my starting move and why I have a FLIR camera on my phone.
It’s very well could be a pressure relief valve jacking off which will cause overheating. If the oil has been heated that hot, stop. Do not run until you find the problem and then change the oil. You will blow that pump up, been there and have seen it many times before. There is a pressure regulator valve and while they are adjustable, they are set to factory specs.
Internal leakage such as bypassing seals or internally worn parts. IR non contact thermometer- look for where it warms up quickest
Charge pressure is normal and it overheat fast under load... I think heat exchanger was collage and operator burns pump and motor once under hight temperature and now it need to be repaired both
Pump is driven by cardan shaft and it have hight vibrations and all pump is vibrating now. So probably now bearings also problem, will open pump and hydraulic motor to check
As mentioned, check temps , find source of heat. If the heat is not migrating out to the cooler and reservoir, your flushing valve is set incorrectly or it is obstructed. Find where the heat is highest, and the lowest. Somewhere in that span, will be your fault.
With the shaft off, inspect the u-joints for excessive play, additionally the yoke on the pump. Does it run true, or is it sloppy on the shaft. Either way, vibration causes wear and heat. Both enemies to your pump. Check driveline angle and verify that your joints are "in phase" Maybe even have it balanced.
The flushing valve is set correctly, and the charge pressure is 13 bar. When the drain line is removed from the hydraulic motor, oil flows out, indicating that the motor is being flushed properly. According to the operator, the mixer was working normally until the day it was used almost continuously without a break. This likely caused the system to overheat, with a clogged heat exchanger being the probable culprit. As a result, the pump, the hydraulic motor, or even both may have been damaged.
How much is coming out of the motors case drain line per minute?
I didn't measured, but under load system is becoming hot very fast, without load works normal
The reason I ask is case drain flow should normally be very low. A symptom of internal leakage on a motor or pump is high case drain flow. I’ve seen motors so toast they fill a five gallon (19 liters) bucket to overflowing in 15 seconds when the spec for case drain flow was 1 gallon (3.7 liters) a minute.
Yeah, internal leakage in the motor would heat the oil pretty fast. Maybe that's the whole issue. The motor needs repairing or replacing. Maybe from being over loaded or over worked. I've had to replace the drive motors in my skid steer. I'd suspect because I've done some heavy digging and pushing with it. I think if all I ever used it for was loading topsoil the motors would last indefinitely.
Yes but it have charge pump which is used to flushing motor and main pump so normal is to have drain flow that is similar to charge flow...
No. Charge pressure is for proportional control, cooling and lubricating. Ideally the pump and motor yield minimal case drain. Rule of thumb, never to exceed 10% of pump volume at rated RPM. For example if your pump produces 10gpm at full stroke at 2100 rpm, your case drain should not be greater than 1 gpm. This is just a generalization but the principle remains.
You are not right friend, charge pump is used also for system flushing and removing heat from system, that is why in closed loop heat exchanger is always connected to drain line. I uploaded photo, there is also purge valve on my hydraulic motor for this purpose. Anyway it is strange I open pump and hydraulic motor and it look good without too much damage. But system heat fast
To clarify, i was trying to help you understand that the volume of the charge pump is NOT what you would see coming from case drain. Yes, charge pressure helps purge hot oil so that it can replenish with cooled but it has other functions. It sounds like the intent or meaning was lost in text or translation
Sure, so from drain line we can have charge pump displacement plus internal lost of piston pump and motor, and if all fine it will be charge pump flow plus maximum 10% of volume of pump and motor ? If I am understanding good
Forget charge pump volume. You said your charge pressure was in spec, you said your loop flushing valve was correct. What is your pumps rated volume at maximum displacement at full throttle. You don't want to see more than 10% of that number . I hope this clears things up.
Okay will measure it
I am going to assume this system is the old Sauer series 20 pump and motor. My experience is that charge pressure should be 1.7-2 bar so 13 sounds a bit low. If a Sauer series motor it should have a purge relief in the motor which acts as a secondary charge relief. This is usually set around 0.3 bar lower than the charge relief in the pump and you should see that drop in charge pressure when the pump is stroked. This also serves as a cooling function as it purges oil through the case drain of the motor and through the pump back to the cooler. These older systems did not usually have a loop flushing valve unless installed externally. If you have overheating you either have inefficiency in your cooling system or you have excessive leakage somewhere in the system. If you have excessive leakage in the rotating groups it will show as significant drop in charge pressure when operating the system.
That is strange for me because charge pressure is 13 bar and I don't have drop of it. I read in service manual that 13bar is normal for this system. Rebuild pump and motor and will see now how system will work.
I checked today without operation charge pressure is 18bar, and when start to operate it drops to 8 bar. And hydraulic motor is more hoter during operation.. so probably something wrong with it
Well, generally when you cook your oil, better get ready to rep your pump.
It is happening after repair.. Can it be that high pressure relief valves on hydraulic motor not good ?
Problem solved, lot of dirt because of pump first time was broken and after repair it stay in system and demaged rotary plates. Grinded rotary plates and it works like brand new.
New problem with closed loop system, pressure will not go above 150bar in one and in another direction 50bar, no case drain from hydraulic motor in neutral and charge pressure is normal 18bar. When pressure go to 150bar low side lose pressure to 3bar, all parts put new in hydraulic motor. Flushing relief valve good, can it be wear of flushing piston ? Because when it stop I have lot od oil from drain of hydraulic motor
LMAO.