Help troubleshooting hydraulic jack

foleda

foleda

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Not directly machining related except that if I can get it working I will use it to move my machines.

I have a pallet jack that does not hold position. I have no experience with hydraulics but lack of experience has never stopped me from tearing into anything before so why start now.

Having disassembled it and finding no glaring problems such as damaged seals or scored rods or cylinders I thought I would ask here to tap the knowledge and experience available on HM before I spend $60+ on a seal kit (more than I have in the entire jack).

The only questionable items I found were a bit of schmutz in the oil and the seals and wipers seem quite hard. Much harder than a 70 durometer o-ring. The seats for the check valve and bleeder valve are hard to see as they are fairly deep within the main casting.

Any advice as to where the problem might be will be welcome.

Related question: What is a good online source for hydraulic seals. Googling the part numbers (NI300 35-45-10 and RSS 10-18/2) turned up a few industrial suppliers of the "call for quote" variety but no online vendors.

hydraulics-1.jpg hydraulics-2.jpg hydraulics-3.jpg
 
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In the past, I have found inability to hold pressure most likely caused by the seal for the pump piston rod. The sideways force causes wear of the seal. In my case, replacing the seal with a new o ring made the jack serviceable again.
 
Unscrew the top of the jack , remove the ram, at the bottom you will find the piston , that may need a new seal. And as RJ says you might need it in the pump. My feeling is take it all apart and go over it. Replace all the fluid and you should have a new jack. If any of the cylinder is scored, you'll have to hone it to repair it, if possible.
 
Another thing to look at is the valve system that holds the pressure. Some jacks have ball bearings that seat with spring pressure
and if the ball fails to seat, it will not hold position. I had one that had rust and basically gunk that caused the pump to not
work properly. Cleaning and new oil was the fix. All jacks operate on the same principle but may vary in design. If you can raise the
jack but it doesn't hold, it is likely the valve mechanism leaking fluid back into the reservoir.
 
The last time I rebuilt my jack, it had the ball bearing system as mentioned above, and I bought the seal kit from these people. They know their stuff, and helped me out in identifying my jack without any ID plates on it. I took a pic of the jack and emailed it to them. You can buy online or call them direct if you have any questions. A normal seal kit is usually around $35.

http://www.toolsandhydraulics.com/shopsite_sc/
 
You can try typing the numbers in the eBay search, if any have been sold it should pop-up. I've done it before it's 50 50 YA NEVER know.
 
Any problem I've had with jacks and hand pumps has been valve related. The seat can get damaged. If so I've had luck drilling the hole below the valve slightly oversize to get a fresh edge, then drop in a ball and hit it one good wrap with a punch. This forms the seat. Toss that ball and a new one seats 99% of the time. You could probably make some sort of lap and rework the seat but I always seam to be fixing the jack 5 minutes after I needed it.

Greg
 
Thanks for all the great advice and information. Sounds like the valves are where I should focus my efforts. I cleaned everything carefully and put it back together and it still leaks down under load. I am going to try lapping the valves next but I am not going to have any shop time for the next few weeks so it will be a while before I can get back to work on it. I'll report my results when I do.
 
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