A Hydraulic Question

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I have an Enerpac hydraulic pump last year off of Craigslist and am trying to get it working now for the hydraulic press that I built.  The cylinder on the press is single acting, there is pressure in only one direction and it returns with a spring inside the cylinder, and I want to use this pump.  When I connect the pump to the cylinder and start the pump it pumps oil immediately to the cylinder extending the ram to full travel.  When I try and retract the cylinder, release the oil back to the reservoir, I get nothing.  This pump is model #PER 3045A and the valve block is a 4 way 3 position tandem center model #VS-4.  This pump has a pendant that has two contact switches, one to extend and one to retract.  There are two solenoid valves that are working (you hear them click when the button is depressed and then an electrical hum if you hold the button down) under the control of the pendant for extension and retraction.  There is a picture similar to the one that I have here: http://www.stifflerssurplus.com/p-46...15v-4-way.aspxThe only diference between the one in the picture and mine is that where they have two ports in use on mine the lower port is plugged and only have one hydraulic hose plugged into the top port, this is how the pump was plumbed when I received it.  I have talked to the Enerpac phone support and they told me that this unit can be used with a single acting cylinder.Does anyone have an idea on where to start with fixing this unit.  I would like to use it as it came with a brand new replacement pump.  It seems like the pump is working fine it is the control giving me problems.  I could take it to a repair facility but would rather learn for myself how to fix this, plus they would charge good money to fix it.Thanks in advance
Reply:Can you take a few pics of the unit you have and post them. Pictures of the valve from a couple of angles.
Reply:From your description, I did not see you list a return line.On standard systems that I work with (not electric) one line from the pump is pressure to the valve.One line returns from the valve to dump oil back into the holding tank.  Without it there is no way for oil to get back to the tank.Did I understand your problem correctly?  Or does your one line serve as pressure and return based on how your system is set up?Dave J.Edit: just remembered some systems have an internal dump on the bottom of the valve.  Does yours?Last edited by MinnesotaDave; 04-17-2013 at 06:11 PM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:From what I understand, you don't have a return off of the selector valve, a return off the pump wouldn't do much as it is a pressure relief. The selector valve will not allow pressure to make its way to the cylinder while trying to retract the piston inside the cylinder. The selector valve will have a spool inside of it to stop pressure flow to OUT port, while opening up the RETURN port that will run back to the reservoir. Once the pump can no longer push fluid through the selector valve, it will return it to the reservoir. Every HYD pump has a return to it. What it sounds like to me, is that you don't have a selector valve between the actuator and pump and that you are trying to use the pump return to retract the cylinder. Also fits that is extends fully as soon as you apply power.Basic Hyd system.PumpActuatorReservoirTubingSelector valveThat port that is plugged could be your return mentioned. Or you have a broken spool that is only allowing fluid through the extension port. But there shouldn't be any movement until you physically move the spool in the selector valve to the 'EXTEND' position.Pictures of your valve, pump and cylinder plumbing would help a lot.Last edited by JWJohnson; 04-17-2013 at 06:57 PM.
Reply:JWJohnson - I see what you are saying, there may be no valve in his system currently.  I did not consider that.Dave J.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:The cylinder in question only has one connection, everything has to come in and out through one line.  The pump provides the pressure to extend the ram and the spring inside the piston retracts the ram when pressure is removed and an open drain to the reservoir is established in the valve (this is my best understanding of the process and is how it works on a manual pump with single acting cylinders).If there is something broken inside the valve, is this just a case of take it apart and see what you find.  Is there anything to be especially careful of when taking the valve apart?  I do have drawing of the part from Enerpac to help.Sorry there are no pictures, I only have the camera on my phone and have not learned yet how and what I need too resize them.
Reply:Originally Posted by JWJohnsonFrom what I understand, you don't have a return off of the selector valve, a return off the pump wouldn't do much as it is a pressure relief. The selector valve will not allow pressure to make its way to the cylinder while trying to retract the piston inside the cylinder. The selector valve will have a spool inside of it to stop pressure flow to OUT port, while opening up the RETURN port that will run back to the reservoir. Once the pump can no longer push fluid through the selector valve, it will return it to the reservoir. Every HYD pump has a return to it. What it sounds like to me, is that you don't have a selector valve between the actuator and pump and that you are trying to use the pump return to retract the cylinder. Also fits that is extends fully as soon as you apply power.Basic Hyd system.PumpActuatorReservoirTubingSelector valveThat port that is plugged could be your return mentioned. Or you have a broken spool that is only allowing fluid through the extension port. But there shouldn't be any movement until you physically move the spool in the selector valve to the 'EXTEND' position.Pictures of your valve, pump and cylinder plumbing would help a lot.
Reply:That description helps.  The valve is hard mounted to the pump unit and has an internal bypass to dump the fluid back to the tank by what I understand you saying.Dave J.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Originally Posted by MinnesotaDaveThat description helps.  The valve is hard mounted to the pump unit and has an internal bypass to dump the fluid back to the tank by what I understand you saying.Dave J.
Reply:Next thing to figure is why the valve lets fluid through the hose without activating that port with the switch.Dave J.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Well I took everything apart, found a broken spring under the pressure adjustment screw and that was about it. I was going to buy the rebuild kit from Precision Hydraulics in Portland and talked with one of the technicians. He told me that getting everything set right when putting the valve back together takes some know how and equipment. He recommended that for using this pump on a hydraulic press to convert it over to a manual valve and then using a momentary contactor to start and stop the pump. The manual valve cost less then the rebuild kit and seems mostly fool proof. Thanks for the input.