Solenoid valve operated dump truck?

Was wondering if anyone has experience with a solenoid operated control valve driven off a front mount pump. It's on a 1994 Ford L9000 that was a plow truck. Sometimes the hoist works great but other times you have to keep trying it to get the hoist to work. It has a Rexroth pump and solenoid valve. I've heard they need pilot pressure to operate but have no idea how to adjust this. It seems to get better if you use it more or I drive a longer distance before dumping. Always has 12 volts when checking with the solenoid activated. Any suggestions are appreciated.

Welder Dave said:

Was wondering if anyone has experience with a solenoid operated control valve driven off a front mount pump. It's on a 1994 Ford L9000 that was a plow truck. Sometimes the hoist works great but other times you have to keep trying it to get the hoist to work. It has a Rexroth pump and solenoid valve. I've heard they need pilot pressure to operate but have no idea how to adjust this. It seems to get better if you use it more or I drive a longer distance before dumping. Always has 12 volts when checking with the solenoid activated. Any suggestions are appreciated.

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You got any pictures of pump , solenoid and plumbing at the pump? We had air and electric operated crank shaft driven pumps on the garbage trucks but really need to see pictures of it to even have an idea how its setup.

You say it has a 12 volt lead to it when activated... but does it change when not activated?.... does it have a switched ground?

Don't have a pic. but it has a driveshaft from the crankshaft direct to the pump. It doesn't look like there's a clutch involved but there is a switch to shut it off. When I tie the toggle switch back it has 12 volts at the solenoid. I've heard the valves can get gummed up and clear up some after using it for awhile. Most of the electrics for the different plows and spreader have been chopped off and the only thing connected is the dump box. There is an electrical box in the top of the cabinet with the solenoid valves and it has a small hyd. hose going to it. I'll have to take a closer look but it looks like it may have something adjustable. I wonder if it's related to pilot pressure? I don't know if it's coincidence or not but giving it more throttle has made it work sometimes.

Am curious to see where this is going. I have a former plow truck similarly equipped and don't fully understand how the hydraulics work. I know that pilot pressure is required for the box to operate.

Here are some pics. of the pump and valves. One large inlet on the pump and a flanged outlet as well as a threaded outlet hose. Maybe a double pump or 1 line is a case drain? l Used the truck today and there were no problems with the hoist. The valve for the hoist has 1 small hyd. hose going in (under 1/2") and 1 larger one. The hoist is the same speed regardless of RPM so I'd guess the small hose is for hoisting and the large line for return oil back to the reservoir. I only hauled a couple loads today but left the truck running while I loaded. The other day I shut it off while loading. I wouldn't think that makes a difference but maybe pilot pressure bleeds off? It has acted up though after driving from my neighbors back field about 3/4 mile away.

Ok that helps some. Your pump looks like a fixxed displacment piston pump . The threaded hose is exactly what you think it is a case drain. I highly doubt you have any pump problems , sounds like its all in the control valve area. Is the main valve electric over pilot pressure, meaning the pilot pressure is waiting at the actuators but the solenoids activate to make it do something. Pump on off switch electric? If so that should dump back to tank when off to circulate oil if that control is on the valve bank and not on the front of the pump? Unfortently i have more questions then answers at the moment . What i would do is if it was mine is figure out where and what the pump on off does and tear it apart make sure its not sticky and is clean, then move on to where pilot oil comes from ,there has to be something inline to limit that pressure somewhere somehow i would not tear that apart but instead tee a guage in to the cab to monitor that when it acts up and take appropriate action to that system if needed. On the main control valve find your dumper valve if pilot pressure seems fine when it messes up take out the electric solenoids and make sure they are clean or swap one of the unused ones from the bank to your dumper circuit to see if it helps . Before i swapped stuff though i would also check the valve bank main relief to make sure it is ok. I would also probably service the system changing any and all filters on it . It is also possible your pilot pressure controlled actuater is leaking past its seals instead of moving the valve. Hope that helps some and makes sense. My systems where air and electric over air to run the main valve and my pumps were crank driven gear pumps but should all be pretty similar in theory.

Pump on/off is an electric switch but I never shut it off. I don't think the pump is the problem either. I believe it is electric over pilot pressure. I think the square looking box in the top of the cabinet above the control valves has something to do with the pilot pressure and electrics. It has a small hose going into it and looks like it could have something adjustable valves or something on it. I thought about switching solenoids with one of the valves that it is no longer used but I thought if the solenoid is bad it would always be bad. That's why checked to make sure it has 12 volts when actuated. Sometimes it takes a few tries to hoist and also can take a few tries to bring the hoist down. If I put a little too much weight near the front of the box, it will stop hoisting when it gets to the 3rd stage on the cylinder. Usually playing with it a few times will get it to go up all the way but I have had to pull some material out to get it to hoist all the way up.

Dont swap just the electric solenoid swap the cartridge valve under it . I would look at the main relief valve on the valve bank and if had access to a flow meter i would hook one up and choke it down to see if the relief valve is working correctly

Might be a solenoid operated unloading relief valve at the top of the cabinet. That piston pump will need some system pressure on it to keep the piston shoes lubricated if it spins all the time.

Engine Off Key ON, have someone operate the switch for the dump control, one you should hear the solenoid engage, two if no noise should become electromagnetic on the solenoid housing, a Small pocket screwdriver is really handy for this. If no noise, no magnetism solenoid is crap, have both the valve is likely stuck/sticky.

One shop told me a couple years ago something can get gummed up but using it more will help to free it up. I wonder if there's an additive I could put in the oil to help clean things up? I think if the solenoid was bad it would always be bad and not work normal sometimes. Any idea how to adjust pilot pressure? The box at the top in the last pic. looks like it could have something adjustable on it. On the bottom right of the same pic. you just see the ears of the mouse I chased out of there. Last thing I need is a mouse chewing on the wires but wiring looks OK.

Also make sure the grounds are all making good connection in the electrical circuit.

Welder Dave said:

One shop told me a couple years ago something can get gummed up but using it more will help to free it up. I wonder if there's an additive I could put in the oil to help clean things up? I think if the solenoid was bad it would always be bad and not work normal sometimes. Any idea how to adjust pilot pressure? The box at the top in the last pic. looks like it could have something adjustable on it. On the bottom right of the same pic. you just see the ears of the mouse I chased out of there. Last thing I need is a mouse chewing on the wires but wiring looks OK.

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Not knowing how exactly the system works ie no service manuals why i suggested teeing in a valve into the cab on the pilot circuit to see what it is doing , i would not go twisting adjustments yet, its not the space shuttle but no sense in causing an a s s ache from improper adjustments .

Welder Dave said:

t giving it more throttle has made it work sometimes.

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Giving it throttle increases voltage and increases pilot pressure.

Check the grounds on the common solenoid

I thought about grounds but if the ground was bad I don't think I'd get 12 volts at the solenoid and I've checked it when the hoist wouldn't work. I wish I knew what everything was and how it's supposed to work. I'm not sure if giving more throttle changes anything because sometimes it makes no difference. If all I had to do was increase throttle it wouldn't be a big deal. Without being familiar with it, it might as well be the space shuttle. I think something is sticking because it does seem to be better if it's used more often.

The ground on the solenoid has nothing to do with getting the 12 volt at the solenoid

If I were you and could not get any kind of manual at all... I'd grad a piece of paper and draw a full schematic of the system layout, that will be a big help in starting to understan how things work.

Your thinking to much about it and not getting your hands dirty, if your not gonna take the time to clean power and grounds and put a guage in here and there are try swapping things from now disused circuits then service the system, new filters and new good brand hyd oil and let it rip . See if it will continue to fix itself with use.

It's not your typical hyd. system. I took a better look at it today and noticed there is also a small line coming off the pump. This line and the case drain line appear to go to some kind of block back on the frame and from the block to the ports on the control valve. The main discharge off the pump goes into some kind of filter and then the inlet of the valve. There are also solenoids on the box at the top of the cabinet. There are a couple Tee's with caps on the line that goes into that box on the outside of the cabinet. All the solenoids appear to have 2 wires going into them. Would the grounds be inside the console in the cab? There are a lot of wires, hoses and electrical gizmo's so it's a little overwhelming for someone who doesn't work on these kind of things. If I had some idea what all the blocks the hoses go into do might make a little more sense of it.