View Full Version : Enerpac won't release

Mike Amick
10-04-2018, 11:09 PM
I had a 391 enerpac hand pump go out and instead of putting out 100 bucks for a couple
small balls and a few little o-rings I bought a pretty newish (yea used) 392 which is the
same pump but two stage instead of one.

I just threw it on tonight, and it definitely moves the single acting spring return enerpac
cylinder a lot faster.

But as the title says it is not letting the fluid back into the pump. I have
not had time to do any checking other than take the cap off which didn't help.

After loosening the release screw I can pry the cylinder back in ... but it will not go back
in by itself.

What may I want to be looking at ? Everything was working fine before the 391 gave out.

10-05-2018, 06:03 AM
Check to make sure your hose couplings are tight.

10-05-2018, 07:59 AM
Also check the hose itself. With age, they'll swell on the inside and close-up. Old automotive soft brake lines did the same thing. That would cause dragging brakes and warped drums and rotors.

true temper
10-05-2018, 12:50 PM
I unknowingly kept pumping with the piston bottomed out. Ram was very hard to get back in, took it apart and the piston was mushroomed a bit dragging on the cylinder walls.

Mike Amick
10-05-2018, 01:21 PM
ok, thanks for the suggestions.

10-05-2018, 02:54 PM
Mike Amick: Did you perchance, in the process of changing the pump (and possibly some hoses), did you wind up with a check valve in the wrong place? Stranger things have happened.


10-05-2018, 03:40 PM
Mike Amick: did you wind up with a check valve in the wrong place? Stranger things have happened.


That also was my first thought.. JR

1/2 dun shed
10-06-2018, 01:44 PM
Are you using the same hose as on the 391 or did another come with the 392? As mentioned before check that the connection is tight. Worn coupling joints can cause this problem.

If you can pry it back in but want retract by itself there maybe a problem with the cylinder. Being a spring return there could be a number of things.
Warning If the ram needs to be pulled apart it must be done carefully. Spring return rams, specially hollow bore can be dangerous.


Mike Amick
10-06-2018, 09:12 PM
Crap. I pumped it up a bit, pulled the hose off and pushed the ball in the coupler and it didn't

Then I pushed the ball in and took a screwdriver and manually pried it up and the fluid shot out.

So its either the return spring or something is getting jammed up.

I can't find any instructions for disassembly & don't want to mess it up. It's an enerpac RC-2510.
Hoping you guys will say how to handle the spring and that every thing else is pretty straight forward.

If it helps, right before this I was using it as a brake to bend 1/4" x 3" wide strips of steel. It was
harder than I usually push it but didn't seem like any problem. I was using a pump borrowed
from my porta power set. And strangely, It continued working until I got the new 392 pump.
And when I swapped out the pump, I only built up a couple pounds of pressure just to test it.

true temper
10-06-2018, 11:58 PM
Are you sure you didn’t extend it out too far under pressure. See post #4 had it happen to me. That was 25 years ago, seems like there was an Allen bolt on the bottom that held the extension spring in. The rod gland unscrewed to remove the piston and rod.

Mike Amick
10-07-2018, 03:09 AM
I don't know. If I can get it apart I can check it out.

Found a blow up diagram

I did unscrew the stop ring (13). Then unscrewed the little cap nut. (12)

It seems like the piston should come out now but it isn't. It's like its stuck on the
bolt that the cap nut came off of. The diagram doesn't even show what the nut is
connected to. I'm guessing its connected to the spring.
Does the whole piston and spring and all come out all together ?

Maybe that roll pin (2) is holding everything.

1/2 dun shed
10-07-2018, 04:23 AM
With top ring 13 coming of indicates that the plunger (piston) has not mushroomed. That's good.
With the cap nut (12) removed you should be able to see a flat screwdriver slot in screw 3.
Unscrew it clockwise half a dozen turns. DO NOT screw it all the way in for now.
With the coupler (17) removed pin 2 should now be loose and easy to remove. If 2 still feels tight unscrew 3 a bit more and see how you go. ()I cannot remember exactly but I think its about 16 turns to undo 3 completely.)
Once 2 is removed the plunger should come out with the spring still attached to it. If it is tight you might have to pump it out. Please do not try and save oil by using compressed air to push the plunger out.(though it is interesting to see how far these things can fly across a workshop.)

Mike Amick
10-07-2018, 12:30 PM
wow .. thanks. I did see that the screw had a slot in the top and noticed that it only wanted to
turn clockwise. But I only turned it a turn or two not wanting the thing to go boing.

Your instructions are perfect ... and I'll try this later today.

thanks a bunch

true temper
10-07-2018, 06:10 PM
My vote is #9 is mushroomed.

Mike Amick
10-07-2018, 11:21 PM
Ok .. that was embarrassingly easy as far as getting it apart once I had a clue.

But I got it apart and wiped everything down and nothing looked messed up. When I got it back
together and tried it out, the piston would take little 3/4" hops while retracting. Like .. not move ..
jump .. not move ... jump. The first couple of times it did go back all the way, but then started stopping
with 3 or 4 inches out.

In this pic you can see the piston sticking out .. and I even took the coupler all the way out.

I did notice that part number 9 that true temper thinks is mushroomed. Its like a brass sleeve split
in two. At least I hope it is suppose to be two pieces.

The only peculiar thing is that it quit working the moment I put the new pump on. I did change the
oil and put in some HF hydraulic oil, which seemed a lot thicker than what was in it.


J Tiers
10-08-2018, 12:21 AM
Thicker oil can mess it up, but possibly not the "jumping". the hydraulic oil is usually really thin.

1/2 dun shed
10-08-2018, 03:19 AM
Jumping can happen when being pumped out or retracting. It is usually caused by air in the system. Lay the cylinder down with the rear slightly raised and the coupling in the vertical position. Connect hose and pump, extent the ram a couple of inches let it sit for a minute then retract. I like to do it a couple of times.


#9 is suppose to be in two pieces so don`t worry. It supports the seal and guides the plunger. I cannot remember ever having trouble with these.


This is what holds the spring to the top of the plunger. The screw that you would have turned in and out to fit pin 2.
The one pictured is from a 50T ram so it might look slightly different to your 25T.
Its not a real problem if this all has to come out, it`s just a pain putting it back together sometimes.

Ok for the ram to go in and out a few times and then stay out is a bit strange. Can it be pushed back in?
Is screw 3 all the way back in putting full tension on the spring? Is pin 2 still held tight?

Mike Amick
10-08-2018, 12:29 PM
Jumping can happen when being pumped out or retracting.

Ok for the ram to go in and out a few times and then stay out is a bit strange. Can it be pushed back in?
Is screw 3 all the way back in putting full tension on the spring? Is pin 2 still held tight?

Yes, it jumps extending and retracting. I will try your bleeding method and that would make sense
going from one pump to another might get some air in there.

I actually can push it back in with my hand but its a pretty hard push and it still jerks.
Yes, I put as much pull on the spring as the screw would allow. And the pin in the bottom
is holding everything nice and tight.

What's your opinion on the thickness of the fluid ?

J Tiers
10-08-2018, 12:41 PM
When I had to make a new valve for the hydraulic downfeed on my Atas bandsaw, The thinnest oil I could get to refill it was way too thick. The thing would not even feed, it sat there, the oil was too thick to flow at any speed.

I ended up using hydraulic jack oil, which worked perfectly..I think itis around an SAE 10. Like slippery water.

The spring return may not work if the oil is too thick.

10-08-2018, 12:47 PM
Is that pump meant to work in the position you have it mounted ?

Mike Amick
10-08-2018, 02:56 PM
yea .. the instruction sheet says horz or vert mounting. I was wondering the same thing so I
looked it up.

And Jerry, I think I am going to change the oil to something thinner.

Is there a difference between hydraulic jack oil, and say mobile synthetic viscosity 5 oil
or even brake fluid or power steering fluid.

I mean they are all fluids designed to do work by being compressed by a pump or piston of some sort.
(well .. maybe not the engine oil)

Just curious.

J Tiers
10-08-2018, 03:46 PM

I just went for jack oil that when I shook the bottle it kinda sounded like a bottle of water.... really thin.

1/2 dun shed
10-08-2018, 05:02 PM
Basically any mineral based oil can be used in these things. I use ISO 68 at the moment because I have about 60 litres of the stuff. It`s about a SAE 20w.
ISO 32 (SAE 10w) (also called Tool oil, Jack oil and a whole heap of other things) is what I used most of the time when I was in the business.

The only difference thicker oil makes is to slow things down a bit. The ram should still retract all the way.

Never (never never) use brake fluid in anything other than brakes. Nasty stuff.

Another one is ATF (automatic transmission fluid, power steering oil), unless recommended by the manufacturer never use it in any hydraulic system. The additives in the oil can attack the seals softening them leading to premature failure.

Mike Amick
10-08-2018, 08:51 PM
Well .. changed the fluid to some real thin other brand hydro fluid and it quit the jerking, and even
(eventually) retracted all the way a couple times.

But .. after a couple successful retracts, it's stopping again about where my pic shows it.

I really should have known. Just looking at my pic .. there is no way that plunger should be
sticking out with the coupler/connector removed.

Something wrong with this thing. I have an enerpac repair facility down the road from me, I'm going
to go talk to those guys and probably spend the 100 bucks for the little bag of seals to rebuild it.

10-08-2018, 08:52 PM
Enerpac and Greenlee hydraulic oil is 10w. I used to sell it