Volvo L120f hydraulic pressure fighting starter motor on hot startup.

[Swannyau]

Hi people, so my L120F has developed an issue with the hydraulic system. The loader seems to not de-stroke the pump when machine is hot? What lead me to this is when I restart the engine whilst machine it's at operating temperature the starter is laboring so much that it barely starts or sometimes won't crank fast enough. I initially thought it may be a connections issue but everything was perfect and it has new batteries. I suspected that it must be cranking against pump load so I cranked and operated tilt cylinder and this allowed it to crank and start easily.

I have looked at the brake pressure via service mode and it is low 160psi and doesn't spike higher when tilt is in overload. The fan speed maxed lower than it should and the cycle times and general movements are slower. It has had the hydraulic system filter and oil change about 250hrs ago. My question is shouldn't the pump de-stroke at start up via the hydraulic power control valve?? If so could this be failing at operating temps, it doesn't have an issue cold.

 

[Swannyau]

So I’m guessing this one looks tricky? I got the following for basic tests on it yesterday. Brake pressure cold 126bar cut in and 150bar cut out and climbs to 161bar with tilt cylinder at max tilt. It doesn’t really lose pressure unless I operate the brake or turn it off for a period. I’m not loosing hydraulic fluid height in tank. The fan test was 880rpm at idle and 1780rpm at max engine revs. Unloaded lift test was 5.7sec from floor to full height. As mentioned it starts and behaves fine until it’s been operated for awhile. I will try blocking supply to quick hitch and diff lock valves and see if I notice an improvement. I did adjust the brake pressure reducing valve and it rose but I noticed the a weep from LS hose from main control valve into the collecting block where SE9107 is so I returned it to as found. Was hoping someone could point me in the right direction as to what may cause this, the machine is a 2017 model with 9750hrs.

 

[funwithfuel]

Ok, from the beginning, you have 3 pumps affectionately known as 1,2 & 3. Pump 1 is dedicated to work. Pump 2 is work and steering depending on need and dictated by the central valve.Pump 3 is brake and fan, again depending on need and distributed by the central valve. You've already done some good basic troubleshooting. Cycle times would've been the first thing asked followed by pressures.
Now to start with, it looks like your pumps aren't hurt because your cycle times are terrific. Your fan speed is good and your brake charging pressures sound perfect. Pump 3, as mentioned does double duty, brake and fan. Regardless of which function, the output is never deadheaded. It either goes to the fan or to the brakes with a trickle going to the fan. So I don't believe pump 3 is your issue. You can disregard any further consumers off the brake accumulators circuit.
Pumps 1 & 2 are different. When you pull a function or turn the wheel, you generate what is known as LS or load sense. This is created when the spool or valve is shifted off neutral. The standby pressure leaks off goes through the central valve and is sent to the pumps from there. Let's say you are only curling the bucket, you are only generating LSW or load sense 'work' that signal goes back through the central valve which has a shuttle valve taking the stronger or higher LS and sending it out to both pumps to do work. Now, from the steering side , you turn the wheel. Again this generates LSS or Load sense steering, which goes back and competes with LSW at the central valve, the higher pressure gets to the pumps. The pumps take the LS and that determines your pump displacement and pressures through the pump compensators.
Either pump 1 or 2 is stroking up when warm, those are the only 2 that can deadhead when neutral. You need to figure out who and why. You'll need a set of gauges. Minimum 6k psi. There should be a manifold under the left or right staircase with test ports marked C L 1 & 2. C & L aren't important now. Focus on 1 & 2. When the machine is off gauge 1 & 2. Normally, the pressure should rise to 30 bar or so. If one or both rise much beyond that, that will tell us where to next. If you have side covers , you'll want to take them off for now. Again youll need gauges and breakout Ts. You can get something similar to this https://m.vevor.com/hydraulic-press...FhyrXDWxRdn-ORHU3zDwNg1ZoAOJ60ShoC_pgQAvD_BwE

It doesn't have to be this big, but if you're gonna be maintaining Volvos, it'll certainly help. Please follow up, we're here to help. Good luck

 

[funwithfuel]

Had a thought last night. You said you pull the boom lever to get her started, that gives the oil some place to go, unfortunately, that gives both pump 1 & 2 someplace to go. Next time, please turn the steering wheel only while starting. If she still deadheads, your problem is with pump 1, if she starts it's in pump 2.
Having said all that, I gotta say this. Please take this machine out of rotation until corrected. Having a pump stroke up unintentionally is very bad. It causes extreme wear on the pump and trans as well as stress on the hoses. There's several of us here that speak Volvo, so you're not on your own. Know this, if the pump grenades, it will cost much more than any loss of production you might suffer.

 

[Swannyau]

Had a thought last night. You said you pull the boom lever to get her started, that gives the oil some place to go, unfortunately, that gives both pump 1 & 2 someplace to go. Next time, please turn the steering wheel only while starting. If she still deadheads, your problem is with pump 1, if she starts it's in pump 2.
Having said all that, I gotta say this. Please take this machine out of rotation until corrected. Having a pump stroke up unintentionally is very bad. It causes extreme wear on the pump and trans as well as stress on the hoses. There's several of us here that speak Volvo, so you're not on your own. Know this, if the pump grenades, it will cost much more than any loss of production you might suffer.

First up, thanks Fun with Fuel. I’ll get guages sorted asap. Without doing further tests I’m leaning towards an issue in the main control bank for the boom. As I mentioned it had that weep at the LS block line from the bom control block thus thinking it’s developed a leak internally? Will certainly report in once I’ve got some guage pressure readings.

 

[funwithfuel]

Is your machine fitted with a 3rd function valve. In other words, do you have 3 levers on the carrier?

 

[Swannyau]

Is your machine fitted with a 3rd function valve. In other words, do you have 3 levers on the carrier?

No, just standard quick hitch.

 

[Swannyau]

Hi guys, so I just got new guage and took some reading as follows.
Cold straight after start up
P1-578 P2-560 and P3 floating between 299-340psi
Reading when against end stroke was P1-1240 P2-3730 and P3 the same.
After releasing control lever the P1 and P2 readings were about the same but rising steadily. They measured 1940psi in time it took me to get from cab back to screwing guage into test points so fairly quick. I then tried a start whilst turning steering but that didn’t unload it so it’s up the main lift and tilt control unit I’m guessing. Waiting on correct tee for testing LS circuits at the gauge block.

 

[funwithfuel]

So far, looks like an issue with pump 1. Low pressure with full demand at stroke end. I have to confirm what pressures should be. You're right though, next step is breaking out and measuring LS. The trick is, we have to do it methodically. First measure LSW, then measure LSS Td in at the central valve. Then we want to gauge the pressure in the hose only going to the compensators. In some cases, the seals in the comp can fail and the pump will self excite. That's gonna require you to pull the floor. You'll need a couple -4 orfs caps and plugs for that.

 

[Swannyau]

So far, looks like an issue with pump 1. Low pressure with full demand at stroke end. I have to confirm what pressures should be. You're right though, next step is breaking out and measuring LS. The trick is, we have to do it methodically. First measure LSW, then measure LSS Td in at the central valve. Then we want to gauge the pressure in the hose only going to the compensators. In some cases, the seals in the comp can fail and the pump will self excite. That's gonna require you to pull the floor. You'll need a couple -4 orfs caps and plugs for that.

Yeah I’m reading through the service manuals but other than the tests and adjustments it’s not a great help. I did recently force a lift and drop against full tilts. Not sure why I did it but this has started since then. Could that blow an o-ring in shock valves ??

 

[Swannyau]

So far, looks like an issue with pump 1. Low pressure with full demand at stroke end. I have to confirm what pressures should be. You're right though, next step is breaking out and measuring LS. The trick is, we have to do it methodically. First measure LSW, then measure LSS Td in at the central valve. Then we want to gauge the pressure in the hose only going to the compensators. In some cases, the seals in the comp can fail and the pump will self excite. That's gonna require you to pull the floor. You'll need a couple -4 orfs caps and plugs for that.

P1 should be 3423 and P2 about 3771 so P1 is 2200psi under it design max. I had it hard against lift arms as I can set that to hold whilst I took measurements. On my own at the moment but will have people here later

 

[funwithfuel]

Yes, it could and does fail o-rings and back-up rings in the sequence valves, but tat wouldn't cause your pumps to stroke up on their own. I think , since you have the manual, it would be best to attempt to set standby with LS plugged. That's the specific name of the operation. I'd like you to set pump 1 & 2. The important thing here is, with the LS hose disconnected and plugged, the compensator fitting should be left open to atmosphere. If any oil comes from those fittings, the seals are failed and need repair. This could contribute to your base concern.

 

[Swannyau]

Yes, it could and does fail o-rings and back-up rings in the sequence valves, but tat wouldn't cause your pumps to stroke up on their own. I think , since you have the manual, it would be best to attempt to set standby with LS plugged. That's the specific name of the operation. I'd like you to set pump 1 & 2. The important thing here is, with the LS hose disconnected and plugged, the compensator fitting should be left open to atmosphere. If any oil comes from those fittings, the seals are failed and need repair. This could contribute to your base concern.

What is the compensator fitting?? The fitting the LS hose connects to at the pumps?

 

[funwithfuel]

What is the compensator fitting?? The fitting the LS hose connects to at the pumps?

Yes, that fitting must never be "plugged" during testing and adjustments.

 

[Swannyau]

Okay done, so the pressure readings with LS feeds capped were P1 - 392psi and P2- 394. Both compensator fitting leaked whilst performing the tests. I adjust the P2 up to 492psi so they are both in range now. Question is could this be the cause or a secondary issue caused by the main problem

 

[funwithfuel]

More than likely, the cause.
When you say ,"both comp fittings leaked" are we leaking under pressure, spraying, or just a dribble? Either way , there should be none, just trying to gauge the severity.

 

[Swannyau]

I also fitted test points to the two LS hoses and checked for build up whilst uncoupled from pumps. The P1 LS line reads 0 until I move a control lever. The P2 LS line showed 50psi and would increase if I used steering and or control levers. Looks like the pump control valves need rebuilding. I’ll contact our Volvo agent tomorrow re parts required.

 

[Swannyau]

More than likely, the cause.
When you say ,"both comp fittings leaked" are we leaking under pressure, spraying, or just a dribble? Either way , there should be none, just trying to gauge the severity.

P1 was a steady stream but not too much, not spraying. P2 was much less but still weeping whilst engine running. Nothing once engine stopped

 

[funwithfuel]

Steering is your issue. Remember, pump 2 supports steering and work. Since LSS is rising on its own you have leakage occurring in the orbital or shift valve. It's sounding like a lot of little issues are stacking up. Can you place your T fitting at the orbital LS port , let's see if oil pressure rises on its own there.

 

[funwithfuel]

P1 was a steady stream but not too much, not spraying. P2 was much less but still weeping whilst engine running. Nothing once engine stopped

There was a bulletin , way back, about improperly assembled comp valve seats. Ask your dealer if they could provide that bulletin to you . It has detailed instructions on how to carry out the repair and what tools you'll need. Plus it shows the part numbers of the o-ring, back-up ring and spool. It's very helpful.