NF Hydro pump acting oddly

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Klapatta
Posts: 1352
Joined: Mon Sep 06, 2010 2:25 pm
First and Last Name: Kenneth LaPatta
Location: Rockingham VT.

NF Hydro pump acting oddly

Post by Klapatta »

Hello all, lately the hydro lift pump that I put into service just over 4 years ago has been acting balky.
When first installed it was both fast and powerful, with an attachment blocked up it would lift the machine off the ground effortlessly.
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There are times when it will lift an attachment right up and others when it is very slow to rise. This does seem to be getting worse since the last time that I used it. One critical thing to note is the response in the action can be altered by engaging the spool valve using multiple attempts as though something is sticking or perhaps partially blocked from the inside.
I'd like to get a better idea of what is going wrong before going into it. By the way it has been behaving I have been wondering if one of the O rings on the spool valve has a blow by issue going on. Or perhaps is one of the check valves acting up. I never have had those out before.
Here is what I do know about it so far:
The belt is set at the right tension and does not appear to be slipping at all
It is not noisy nor is the shaft loose
The spool valve and operating handle are not binding and the action returns to center correctly so the centering spring is not broken
The oil chamber is full. The oil is not milky but is by no means a golden amber color anymore either. I have been using Mobil DTE #25 which is a high grade ISO 46 viscosity (20 weight) hydraulic fluid. It does require a couple tablespoons of oil a year.
I have been thinking about doing a fluid change first before going into it. Other than pumping it dry I'm not really sure how to get all the old oil out of it without taking everything off the machine.
These units are pretty simple inside but rather than a taking a total tear down approach I'd like to isolate the matter first as it does work.
Can anyone report an issue such as this and what did you find to correct it?
Thank you

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BigMike
Posts: 1351
Joined: Mon Sep 06, 2010 8:45 pm
First and Last Name: Mike Andrews
Location: Niles,Michigan

Re: NF Hydro pump acting oddly

Post by BigMike »

My vote is a piece of something getting in the valve barrel ports. Floats around in the fuid and is no issue then all of a sudden it gets in just the right spot and causes your issue.

Paulf
Posts: 190
Joined: Wed Sep 08, 2010 9:20 am
First and Last Name: Paul E. Funk
Location: Boonville, Indiana

Re: NF Hydro pump acting oddly

Post by Paulf »

Kenneth, there are no check valves in the system and only one O-ring in the valve body itself. http://www.cubcadetman.com/cc/how-tos/h ... lic-pumps/ I wonder if you don't have some dirt in the relief valve. It's located on the side of the body of the pump. I'd check that first before tearing into everything. Hope this helps.

Klapatta
Posts: 1352
Joined: Mon Sep 06, 2010 2:25 pm
First and Last Name: Kenneth LaPatta
Location: Rockingham VT.

Re: NF Hydro pump acting oddly

Post by Klapatta »

So it sounds like that I have to take a look at the relief valve. It's held in place by a slotted screw. I was never able to budge that screw so I left it alone.
It's location is circled.
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I should mention these are saved photos from January 2013.
This has to be the pump and not the cylinder, the machine can sit for weeks at a time with a heavy thrower mounted in the upright position and it will never drop one bit.
There could be a speck of dirt holding the ball open or there could be a ridge line of wear on the ball.
When it wants to lift up fast it will, it's action is very random.
I just took a look at it and the slotted screw is facing inward toward the flywheel shroud so there's no getting at it without removing the pump.
It is still working and this is starting more to sound like a fair weather job.
An oil change would be the first thing on my list first I think. While always covered it stores outside and water condensation may also be an issue. The canister can be cracked open while it's on the machine to drain and the cylinder can be bled by cycling the piston manually with one hose removed.
Thanks for the tips guys.

Klapatta
Posts: 1352
Joined: Mon Sep 06, 2010 2:25 pm
First and Last Name: Kenneth LaPatta
Location: Rockingham VT.

Re: NF Hydro pump acting oddly

Post by Klapatta »

Update. I cracked the canister open with the unit on the machine. The oil had a very dark appearance but not milky or metallic in any way. Also, It's possible that the oil level was lower than I had thought. I did not bother bleeding out the cylinder though, figured a half a change is better than none. Replaced the oil with the same fluid that I had been using. The unit is performing properly now, it seems very responsive- right now I think that's all it needed.
80 degrees here today so I'm thinking mow the lawn now. ;)

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