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I am needing assistance with an excavator hydraulic system.

HI Pearl, I...

HI Pearl, I am needing assistance with an excavator hydraulic system.

Mechanic's Assistant: Sometimes things that you think will be really complicated end up being easy to fix. The Heavy Equipment Mechanic I'm going to connect you with knows all the tricks and shortcuts.

OK, thanks.

Mechanic's Assistant: Are you fixing this yourself? What have you tried so far?

Yes, I am in the troubleshooting stage and plan on repairing myself. So far, we have determined that the hydraulic tank is at correct level, filter screen is clean, and have one cylinder that is dripping at seal around rod on crowd control.

Mechanic's Assistant: Anything else you want the Equipment Mechanic to know before I connect you?

The issue with system seems to be that there is not enough hydraulic power to operate any of the joystick functions. Machine seems to move cylinders (although very little) at idle speed better than at a higher throttle position when all functions seem to do little of anything.

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Answered in 1 day by:
6/3/2020
Mechanic: Dan, Technician replied 2 years ago
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 14,875
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Hi,It is Dan. I will be glad to help. We can follow up as needed on here, Give me some time to review your information and follow up with my responses. Professionals are not employees of the site but users of the site and help on here as time allows in between jobs,family,etc. Response time can vary depending on my work load each day but I will always respond back on my next available login. Feel free to respond back at anytime if for any reason we seem to get separated,for status, etc.

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Mechanic: Dan, Technician replied 2 years ago

Excavator hydraulic systems can be some of the most complex hydraulic systems. Depending on the make model and serial number of your machine, will depend on the actual design of your hydraulic system whether it is load sensing hydraulics, etc.. When troubleshooting a hydraulic system such as this, it is best to have the proper hydraulic schematic for the machine you are working on and its serial number break. You should also have pressure testing gauges as well as a hydraulic flow meter. The gauges are relatively inexpensive but flowmeters for a hydraulic system such as this can be very expensive and usually owned by equipment repair shops. To cover some initial steps of checking and testing that can be done initially without this testing equipment would be to check inside your hydraulic filter and hydraulic suction screen for fine metal and debris that looks like glitter in the oil and filter which would indicate a main pump or component failure occurring since it seems that all functions are being affected. Some of these hydraulic systems on excavators have a separate pilot pump at the end of the two main pumps that are coupled together for two pump flow that is split between your functions on your machine. The pilot pressure is your control pressure that shifts the spools on the main control valve to then open the ports out to your functions. A lot of the newer machines do not have a separate pilot pump but a pilot pressure reducing valve to get your pilot pressure for control pressure. Usually the machines with pilot controls have a separate pilot strainer at the rear area of the hydraulic pump in the pump compartment. Check inside that pilot strainer for signs of metal or debris as well that would indicate a faulty or failed pilot pump. If you lose control pressure, there will not be enough pressure for your control circuit to shift the spools to get the functions to operate. Your main pumps split all of your functions in half. You have one pump controlling one side of your travel and the other pump controlling the other side of travel functions. You also have one pump controlling one half of your functions while the other pump controls the other half. Therefore, if you are experiencing loss of all functions, you will want to verify pilot control pressure to your pumps and main control valve. Also check your control valve for any signs of metal or debris as well as your pressure relief valve cartridges within the main control valve for any debris, damage, or damaged O-rings that would cause a bypass of pressure and the inability to obtain full circuit pressure. All of these procedures are also going to vary on your make model and serial number of your machine as well because there are different variations to the hydraulic system based on the make model and serial number machine. It's a pleasure to help anyway I can.

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Customer reply replied 2 years ago
Thanks for the reply, Dan. Leading up to the request for help, we had already determined that there were no flakes or particles in oil strainer assembly, but had not checked at the main pressure relief valves. I'm assuming that these are located on the main valve assemblies. I will check those in the morning and see what is there. To help with understanding the system that we have, I will give you the brand of machine and give you my best description of what I am seeing around the pump/pilot pump area. The excavator is a German made Schaeff, model no. HS40. This is a walking style excavator with a lot of functions that are usable with changing of a switch or movement of lever. It appears to be equipped with a two pump setup, and a small pilot pump at rear of main assembly. There are several small lines from pilot that lead to a section on side of the main pumps and then tee off to appear to run into the cab area. Not sure if this means it is load sensing or not. Like mentioned earlier, functions work better during cold start up as compared to 15 mins after warmup. But, regardless of oil temp, the machine will barely move any cylinder (if at all) and far sure will not operate multiple controls at same time. It will move functions better when at idle than when at increased throttle. I have not been able to come up with any Hydraulic schematics or any printed material for the excavator, possibly due to not being a popular brand here in the US. From troubleshooting that I have done already, there is nothing that I can visibly see that seems to be broken, although there is one cylinder (crowd) that has a rod seal leaking fairly good, but not spraying. Had a thought about possible seal damage inside this cylinder allowing oil to bypass and pressure up backwards through control valve, but doesn't seem feasible due to all functions being affected even when the crowd cylinder is not being used. There are several ports that look like pressure gauge could be attached, but I don't have any to install for testing. Where would one purchase a suitable gauge and what would the pressure rating need to be for testing in this type of system? Thanks for taking the time to assist with this issue. DKE
Mechanic: Dan, Technician replied 2 years ago
Thank you for the update on the system you have and machine. You are correct as far as information being scarce here in the US for this model machine. It would be hard to say what the exact pressure specs are without the actual shop manual for this machine as they can vary quite a bit. You can purchase gauges either online through Amazon and also through your local hydraulic hose and fitting shop like the Parker store. 4 pilot pressure you can usually expect to see a ballpark of around 500 PSI to the 550 PSI range in a hydraulic system. Now this is a common range but not your particular specifications.you will at least be able to see if you are anywhere near that range or if there is an obvious pilot pressure problem. Main pressures going out to your functions can run anywhere from around 2500 PSI on a smaller machine up to 6000 PSI. You will want to get a gauge that reads double the pressure you were seeking for most accuracy.For your pilot pressure I would get about 1000 PSI gauge and for your main pressure it would be a good idea to get a 10000 PSI gauge. You can also get a 5000 PSI gauge for any pressures that are around 2,500 to 3000 psi for the most accuracy. The kits you can buy online have the spaghetti lines which I really thin lines that allow you if long enough to actually have the gauges in The operators cab with you when testing. You will need to identify the test port fittings and if there are no test port fittings on this machine you can buy some tee fittings at your local hose & hydraulic shop to adapt your gauges in line. You would then deadhead the circuit or function you are testing with the throttle at full rated RPM to get your pressure reading. Make sure you are safely away from any buildings or anything when testing pressures.
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Customer reply replied 2 years ago
Just saw your response, Dan. I will check with local hydraulic shop for pressure gauges and fittings in the morning after a check of the main relief valves on each spool block. Will be in touch when I have more info. DKE
Mechanic: Dan, Technician replied 2 years ago

Sounds great and you're very welcome.

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Customer reply replied 2 years ago
Hello again Dan, I am still chasing this issue with hydraulics on Schaeff HS40 excavator. Will be in touch with you for additional info when I am able to test the hydraulic circuits upon arrival of gauge/test kit. Thanks DKE
Mechanic: Dan, Technician replied 2 years ago
Thanks for the update. You're very welcome.
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Customer reply replied 2 years ago
Dan, got the gauges in yesterday to test the pilot and main circuits. So, after checking right off of the gear driven pilot pump, I am only seeing about 100-150 psi. 200 was achieved at higher working rpms when first warmed up. . From the main pump, I am seeing 0 psi with no circuit activated and(###) ###-####when circuits were lightly activated. So, the issue appears when any circuit is activated more than just lightly. At that point, the main pump pressure just falls off to zero until you let off and do it again with same result. We're trying to determine why the main pump pressure falls off but without hyd schematics, I can't really determine flow to understand what is telling the main to quit pumping and then start again when circuit activated. At that point there is no sudden change in pilot pressure or not much anyway. Pilot does fall off to under 100 when warmed up and idling. That's not much info I know, so hoping you could help shed some light on it or steer me in right direction.
Mechanic: Dan, Technician replied 2 years ago

If that is a gear type pilot pump and you are only getting 100 psi to 150 psi, that sounds considerably low to me for pilot pressure as most hydraulic circuits that I have worked on with a pilot type system operate anywhere between 450 to around 600 psi on pilot pressure. It is very possible that the limited pilot pressure that you have is not enough to shift the spools on the main control valve to open the ports and send main pressure out to your functions. There is still a possibility that you could have a main pump pressure problem but it is also possible that this all could be related to just the lack of pilot pressure. I would have to say that for starters if you are finding no metal or debris within your hydraulic system and filters, I would look at a pilot pump replacement but also see if maybe there is a pilot valve block from that pump that has a relief valve as well that is adjustable and inspect that valve block to see if there might be pressure bypassing within it.

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Customer reply replied 2 years ago
Any idea of what would make the main pump pressure fall off when fully activated? Does the pilot pressure control the main pump pressure? Gonna check to see if relief valve is in line on pilot pump and check it out first. Any idea where the schematics could be found?
Mechanic: Dan, Technician replied 2 years ago
See that's the thing, depending on whether you're hydraulic circuit is set up for load sense or pressure compensating which works off of negative pressure to adjust pump flow rather than pilot pressure to signal the pumps. Or you can have just straight pilot pressure that shifts the spools on the main control valve. This is an oddball make machine as I'm sure you are aware already. The only suggestion for any manuals is a Google search on the web or eBay for any possible used manuals kicking around unless there is still a dealer somewhere that is possibly still in existence.
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Customer reply replied 2 years ago
Hello again Dan. Still been looking and trying to understand my issue with this system. No change in pressures even after cleaning and looking thru various valves thru-out the low pressure pilot pump arrangement. Havent changed the pilot, but looking to do that this weekend. I have adjusted the relief valve on main body to see if that would help from the pressure falling off instantly, but moved it back to original setting when nothing changed for the better. Also, adjusted the compensator on pump same way with no change either. So, I am back to the original (?) settings on these components without them helping at all to alleviate the issue. Just to help my understanding, how does the negative pressure system work that you mentioned earlier? Does this type of system use pilot pump pressure in conjunction with a compensator built in to the pump body? Thanks for being patient while I work thru the system.
Mechanic: Dan, Technician replied 2 years ago
Thank you for the update. Unfortunatelyortunately this goes back to my original advise that this machine has very limited support in the United States and you really need a hydraulic schematic for this model and serial number machine when getting in this deep. This is not an easy one for sure especially where this is not your typical excavator in the United States. There are several types of hydraulic systems that have been used on excavators which are also some of the most complex hydraulic systems on equipment. A schematic is going to be very important to obtain as well as your pressure specifications for testing. It's a little more difficult road but you could always check the pump tag as well to see what make and model pumps are on the machine and try to identify the system that way but I think my first step would probably be to reach out to Terex technical support and see if they can email you some schematics and pressure test information on this model.
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 14,875
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Customer reply replied 2 years ago
Thanks for the info, Dan. I will reach out to the Terex dealer or try and get ahold of a dealer across the pond to try and obtain the schematics. Thanks for all your help with this and I will let you know what I come up with.
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