Looking for some help on diagnosing a problem with a Auto Crane 5005H. So this unit came off a service truck but we set it up in a shop. It has 2 cylinders to lift and extend the boom and it has 2 hydraulic motors to wind the cable and turn the table. So we have a continental hydraulic PVR6-4B20 hydraulic pump mounted behind a 5 hp electric motor. This pump can supply .7 cubic inches per revolution and 2000 psi at 1800 rpm. What we are experiencing is the pump stalls the motor off before we can even adjust the pump to have more then 500 psi. I assumed the relief valve in the main control valve for the crane is enough or do we need to install another relief valve before the control valve? Any help is appreciated.
Is there a system relief in the control valve? Most DC power packs which I assume this originally was paired with, have the relief built into the power pack or actually in the pump itself in my experience. Is your motor for sure 1725 RPM? If it's actually 3450 RPM you're hooped, will need a pump half as big. You'll need 6 HP to push that pump to 2,000 psi at 1725 RPM, but your 5 horse may do it intermittently on overload if your wiring can handle it.
Lantraxco, The control valve allows oil to return back to the tank which i assumed meant it had a relief valve but I could very well be wrong. Yes, this unit originally came with a DC powerpack which we did not get with the crane. The motor we run is 1725 RPM and according to my calculations it should at least be able to push 1800 psi at 5.4 GPM which is what .7 cubic inches per revolution works out to. What does a pump do when a circuit does not have a proper relief valve? Does it not build up pressure and stall the motor?
Actually it should be 5.227 GPM at 1725 rpm, and that flow at 1800 psi will cost you 5.489 HP. Not accounting for efficiency losses. The manual I looked at shows a separate solenoid operated dump or proportional valve with the system relief in it, does not appear to be part of the main valve manifold, got any pictures?
Autocrane manuals available online: http://www.autocrane.com/html/resources-legacy-manuals.php . Looks like 5005H is a pto hydraulic unit and had the system relief valve installed on the hydraulic tank on the return side. 5005EH would have the electric hydraulic power pack and the relief valve would have been in the power pack. Either way, it sounds like you don't have a system relief valve on the crane, but do have open center solenoid valves, which is good. You mention adjusting the pressure of the pump. Normally, I would think of adjusting the pressure at the system relief valve. What is on the pump to adjust? Some more information would be helpful: where are you measuring the pressure? by stall do you mean it actually stops the motor from turning? when does it stall: without solenoid valve actuation? with actuation? with actuation and cylinder at end of stroke? Could electric motor be weak? Is it on phase converter? etc.
Biggest difference is that the DC power pack only comes on when you push a control button, whereas the ac motor is running all the time with no where for the fluid to run.
OK so this is the pump and motor. That threaded rod on top is actually a pressure adjustment not a relief valve like i actually thought at first. This pump is a vane pump where the ring can be moved this is threaded rod to adjust the pressure.
And this is the side of the crane.
this is the control valve on the back of the crane. It has dc powered electric solenoids. they work but we dont have the switch to control them. but the valve has a little knob where a quarter turn and pull opens the valve and we control it like that.
side view of the control valve
OK so i will add a little more to the story now. A buddy had this wet kit lying around and he let us try it on our crane. it was just a matter of connecting the hoses to the control box and bam everything worked just perfect. the motor and pump were not straining at all to lift 1500 lbs. I found the same manual online and noticed that the crane has a relief valve. but we did not get that valve when we got the crane so that must be the issue I am guessing since the wet kit i borrowed from my friend probably has the relief valve built in.
no back to answering some questions. measuring the pressure just out of the pump. you can see the hose we used on the first pic to measure the pressure. no activation causes the pump to stall but only after adjusting the pump to about 500 psi. if we back off the adjustment rod on the top of the pump it works but does not have the power it needs to lift anything. so not valve activation causes the stall. if we open a valve and adjust the pressure higher it works but only until we close that valve again and then it stalls again.
I think that if your problem was not having a pressure relief valve in the system you would be experiencing excessive pressure problems, not lack of pressure. I would be looking at your vane pump as the culprit. Do you have experience with this power pack in other applications to know that it works correctly? If this is a variable displacement pump and there is something wrong with the regulation perhaps you are pumping so much oil that you can't get above 500 psi with the power you have. Not too familiar with this type of pump, but I would start with some basics like verifying correct pump rotation, finding a recommended initial pump pressure screw setting (something like turning in the screw until you feel spring tension and then x number of turns), checking for broken spring(s), checking to make sure you are not sucking air into the system, etc. If all else fails, a gear pump can be purchased fairly cheap on ebay that would be suitable for what you are doing.
The 5005H used a PTO pump and had a solenoid dump/relief valve. You can easily make up one, just a solenoid valve that dumps oil flow back to tank until it's activated and plumb a three port relief valve into the pump line before the dump valve. When you connect up your controls to the individual solenoid control valve coils you wire a diode to each hot wire and then splice all those wires down to one that connects to the dump valve. That way if you activate any function it closes the dump valve and pump flow goes through the control valve manifold. I think I said that right.
brianbulldozer, my thoughts exactly on the relief valve in the system. the pressure should be on the higher side instead of the lower side as it stalls the motor. I am not familiar with this pump and I have a friend who is pretty good with hydraulics and he hadn't come across this type of pump in the 25 years he'd been working on machinery. we did take the pump apart and the valve plate is positioned correctly with the rotation of the motor. it is possible to have backwards but not this case this time. we were thinking of checking the volume. like taking the line that runs back to the tank and seeing how many gpm are actually passing. lantraxco, I do not have these types of parts just kicking around. I will call upon my friend in hydraulics and see if maybe he would have these valves lying around and we could plum them in. If he does not have, where would you get them?
Reliefs you can pick up anywhere, something like this would be fine: http://www.surpluscenter.com/Hydrau...-16-GPM-1000-2500-PSI-RELIEF-VALVE-9-1556.axd You can use a normally open valve, tee it into the pressure line: http://www.surpluscenter.com/Hydrau...FORCE-12-VDC-N-O-SOLENOID-VALVE-9-5112-NO.axd Assuming your existing valves are set up for 12 volt.
If it worked with your buddy's pump, then I'd take your pump off the crane and test it alone before adding more parts. Run the pump with a line going straight back to the tank, if that runs add a gauge and a valve with a blocked port and close it SLOWLY, if you can't get it to build 1,000PSI, then get a different pump. Is that a directional valve on the pump in #11? If it was running as an open center valve with that pump, then why do you need anything else? I don't think the dump valve is needed, that would be for DC use. The relief valve is needed, to keep stuff from popping at a very bad time.
Delmer, yes that is a directional valve on my buddy's pump. worked just fine. I think i will just get a setup like what he had and put that on the crane. Brendan
So with none of the control valves activated it stalls the pump, which means the oil is not being returned to tank, the pressure port is blocked in the manifold. The oil has to go somewhere, you're probably lucky not to have ruptured a hose or the pump.
This could happen if the crane was designed with closed center hydraulics, and the hydraulic pump on the original wet kit was variable displacement pump. Read up on "closed center" vs "open center" hydraulics. http://talk.newagtalk.com/forums/thread-view.asp?tid=43514&mid=309980#M309980 Please note that if you use a relief valve to connect a gear pump to a closed center system, shortly you will overheat the oil.
I have the same model crane and the valve that was on the tank. If there's anything you need to figure out by looking at another crane I'll be happy to help.
Steve328, the problem with the unit ending up being the electric motor. We bought a new one and installed it and the crane has been working ever since.