Splitter Hydraulic Question Revisited

[NCMau]

I did post a "Splitter Hydraulic Question" on 1/11/10. I installed a new pump (16 gpm ) but it did not solve the problem. The system is still not developing more than 500/600 psi at input of valve. It looks like the second stage is not kicking in.
(5 HP electric motor, 3600 rpm, 5" cylinder, 16 gpm pump) This a home built splitter and worked just fine for the last 10 years.
I replace the fluid and tried to adjust the valve automatic return (detent?) with no results.
What is next? The cylinder?
I don't know if it is normal, but when the cylinder is at rest in retracted mode, it advances 2-3" before it stops. Also when the cylinder reaches the fully retracted position, the gauge shows 500-600 psi until I bump the lever handle. Then it resets.
Is the valve the problem area? I am more inclined to believe that the cylinder could use repacking, but I hope I am wrong.
Suggestions?

 

[J_J]

If that pump is a two stage pump, you should read up to 650 psi while splitting light weight wood, and when it gets to the end and you hold the lever forward until the relief goes off, the gage should read 2500 psi. If the valve is bypassing, you will not be able to get a good pressure reading. Do you have another valve to test out the pump?

You could put a ammeter on the electric motor, and see if it is even drawing a load.

Could be bad pump, bad valve, bad cylinder. Have you eliminated any of those?

To positively check out the pump and valve, remove the pressure hose going to the valve, and put a needle or gate valve on the end and connect another short hose from the needle valve to the valve. With the needle valve open, start closing the needle valve and see if the pressure builds up, DO NOT close off the the needle valve all the way, or keep it at high pressure. If things are working right, . This will add a restriction to the pump. If the pump and is good, then you should see 2500 psi on the gage at some point. To see if the work port has pressure, put a gage and needle valve on the A work port, The hose from the work port should go to tank, then, activate the lever to see if the valve will allow pressure to build up. Again, you are adding a restriction to the valve circuit to test the valve.

All we know so far is that you changed to a 16 GPM pump, assuming that it is good. The above test will prove that.

It is not normal for the cyl to advance in neutral . If the cyl moves, the valve is leaking, or there is an air bubble in the cyl, which is unlikely.

 

[NCMau]

J.J.
I did the valve test and did get the 2500 psi with the restriction and test gauge. Also, since the built-in gauge showed 2500 psi, can we assume the pump is also okay(?) (specially since it is new).
So what's left? The cylinder? The cylinder is an old military surplus at least 40+ years old, it just maybe having internal problems. There is a small external leak, but nothing significant.
Is there anything also I should look at before I take the cylinder to the hydraulic doctor?
BTW, the motor amp draw is where it should be.

Maury

 

[kennyd]

The piston seals could certainly be leaking internally so pressure can not build up behind the piston.

Simple test: Remove the hose from the rod-end of the cylinder after its extended all the way, now try to extend the cylinder further with the valve-if fluid comes out of the open port, the the piston seals are definitely bad.

 

[J_J]

Maybe the piston has come off the rod, or very loose.

 

[woodsroad]

Maybe the piston has come off the rod, or very loose.

That would account for a leak at the main seal. The ram is no longer true in the cylinder if the retaining nut is loose. I would refrain from testing the cylinder any further (since the ram may be loose) and get it looked at.

 

[banjodunn]

G'day check your cyl as it sounds like your piston seals are us the safest way to check is to extend/ retract cyl fully remove both hoses and plug compressed air to the port full of oil and see if you get air/oil out the other port much safer than using the hyd


Jon

 

[oldnslo]

Where is the system relief valve located? In the directional control or in line between the pump and motor?

If you can build pressure with a restriction located between the directional valve and the pump the pump is operating correctly.

Simple test for bad cylinder. Remove both hoses from the cylinder and plug these ports on the valve. if you build pressure now it is a cylinder problem. If you still do not build pressure it is a valve problem. I would look at the system relief to see if a piece of dirt has jammed it open. These are typically shimmed so be careful you don't loose shims during disasembly.

I Would not operate the cylinder any more until I determined where the fault is. If the rod and piston are seperating you could possibly damage the cylinder bore by trying to cycle it more.

Roy

 

[AKKAMAAN]

Where is the system relief valve located? In the directional control or in line between the pump and motor?

If you can build pressure with a restriction located between the directional valve and the pump the pump is operating correctly.

Simple test for bad cylinder. Remove both hoses from the cylinder and plug these ports on the valve. if you build pressure now it is a cylinder problem. If you still do not build pressure it is a valve problem. I would look at the system relief to see if a piece of dirt has jammed it open. These are typically shimmed so be careful you don't loose shims during disasembly.

I Would not operate the cylinder any more until I determined where the fault is. If the rod and piston are seperating you could possibly damage the cylinder bore by trying to cycle it more.

Roy

If piston is fully separated from the rod, the rod will come out at full extention....and so would a lot of oil...
BUT if the piston is fully separated from the rod, the would not be possible to retract the rod.......

I would check out the main relief in the directional valve.....screw in is usually increasing pressure....so try that, screw in and out, while pulling lever till cylinder stalls, and see if gauge reacts on it....

 

[AKKAMAAN]

To positively check out the pump and valve, remove the pressure hose going to the valve, and put a needle or gate valve on the end and connect another short hose from the needle valve to the valve. With the needle valve open, start closing the needle valve and see if the pressure builds up, DO NOT close off the the needle valve all the way, or keep it at high pressure. If things are working right, . This will add a restriction to the pump. If the pump and is good, then you should see 2500 psi on the gage at some point. To see if the work port has pressure, put a gage and needle valve on the A work port, The hose from the work port should go to tank, then, activate the lever to see if the valve will allow pressure to build up. Again, you are adding a restriction to the valve circuit to test the valve.

This is an EXTREMELY DANGEROUS ADVICE!!!!
Note that there is NOTHING that protects for over pressure.......This is like using an old Webster flow meter, with out the safety soft brass washer that cracks at over pressure......I have cracked one saftey washer on a Webster.....and it was not fun at all........


What people do not realize, is that a needle valve get very progressive the more closed it gets....while wide open you might have to turn it 1 full round, for a 200psi increase of pressure....but at 2500psi, less than 1/4 turn can pop the pressure to 5000psi or more....it all depends on needle valve characteristics and pump flow....

IF something goes wrong turning that needle valve....you might have 4000-8000 psi at a burst and could get killed or severly damaged from oil injection, and "grenade" splits.....

If you want to do this test, you must put an inline Relief valve between the pump and the needle valve.