1850 Hydraulic pressure pulsates - any theories for cause?

[MikeOConnor]

Hi all,

I've just laid down a huge time-consuming piece of volunteer work which means I have a lot more time to get in trouble with my 1850.

So today I decided to do the routine maintenance and replace the hydraulic filter. When I fired up (after bleeding), the hydraulic pressure started pulsing. Normal is around 1500 PSI, the pulse-range is between 1300 and 1700, about once a second. Here's a link to a 7-second Youtube video that shows what's going on.

https://www.youtube.com/watch?v=m2-dF9ZIkfg

So I bled it again, just for good measure. Same deal.

This happened once before and the theory then was a blown seal in the pressure-relief valve. That valve is dry as a bone this time, and the only thing that's changed is a new filter.

Is this something that somebody's seen before? Just curious. I'm planning to call Terry on Monday, but just curious to see what TBN folks have to offer.

 

[cqaigy2]

Possibly air is be pulled in from somewhere? When you bleed, im assuming no air whatsoever? I had an issue with the filter not being set down well and it would pull air when i was bleeding the system. I'd lubed the seal on the filter good but just needed about 1/4 turn more.

 

[MikeOConnor]

Thanks for the tip. I'll have a go at reseating that filter tomorrow and see what happens. Bleeding didn't have any air in it, but there's a lot more oomph when the PT is actually running rather than just cranking over. I would love that as the fix.

 

[woodlandfarms]

Weird, I would agree with checking the filter but you would think you would see foam if this was the case. It might also be a bad filter.

 

[MikeOConnor]

Dang, that simple fix didn't pan out. I reseated the filter and bled it again. Still pulses.

I kinda like the "bad filter" idea. Unfortunately this is the last filter in the box so I can't try that idea out today.

Any other theories people want to lay on?

I'm wondering if something else is failing -- and if so, how do people go about isolating various parts of the hydraulic system to narrow down the cause? Is there a tried and true way of capping off various circuits one at a time?

 

[marrt]

Well, that is very odd. It's almost like a relief valve is cutting on and off. What about disconnecting the PTO switch or value. Not sure about the engine bay configuration on an 1850 but maybe you're getting a short or something related to the PTO...since you were in the engine bay to change the filter.

 

[KentT]

Out of curiosity, which hydraulic circuit is showing this pulsing?

 

[ponytug]

Dear Mike,

Since all you did was change a filter, I would go with the air leak or bad filter. I have once had a filter that required 3-4X the normal force to seat properly. An examination of the o ring and can didn't show anything obvious to the naked eye, but the pump cared. I noticed mainly by oil misting out of the cartridge.

Are you seeing mini bubbles coming back into the hydraulic tank? At some point, you would be getting air back through the case drains.

If not, it may just be that something else failed at the same time. Is it possible that you have the draft control on, or that the automatic brake circuit is in trouble (that should kick in about 500psi, so it seems like a stretch.)?

Good luck!
All the best,
Peter

 

[MikeOConnor]

Hi folks. Thanks for the thoughts...

- the relief valve has been a problem child on this machine for several years. I think I'm on my 4th or 5th rebuild (I think mostly because it dies during really cold weather work - like 0 to 10 degrees). But in the past it's failed by blowing seals and then leaking. This time around it's behaving pretty well -- nice n'dry.

- the pulsing starts as soon as I start the PT -- I can hear that slight variation of engine RPM. But I don't know how to determine which circuit is actually where it's pulsing. Is there a good way to figure that out? That would help immensely.

- I really cranked on the filter this time around, thinking that might seat it better. I don't see any leakage from around the filter, it stays dry too. So I'm thinking that something else has coincidentally failed too. I've got the mower hooked up, so the draft control was on. I disconnected the mower and turned off the draft control, but that didn't do it.

Terry has something to try -- this happened to me once before and he told me something to do, but I forgot to write it down so I'll ask him again tomorrow morning. Last time around that didn't work either and we replaced the pressure-relief valve.

I think something else is failing and stressing the whole system. The hydraulic pressure often "hangs" up around 2500 PSI. A quick flip of the Brake Tender clears it up. That's not the same problem, but whatever is causing that may be why the rest of the system is over-stressed and failing in these flaky ways.

 

[ponytug]

Dear Mike,

Thanks for the extra details. It sounds like either a pressure relief or the automatic brakes are acting up. I'd be interested to hear what Terry has to say.

All the best,

Peter