'93 Monaco Dynasty blowing spin-on inline hyd filters

Hopefully a hydraulic engineer with some knowledge of RV hydraulics will post and can describe if there is some type of pressure regulator that can be adjusted or replaced. I'll just throw out some things in the meantime.

Out of curiosity, what brand of filter are you using. Is there an OEM filter available and have you tried one. The reason I ask is that some spin on filters have a built in bypass. Possibly, a cheaper quality filter may not.

What is that pump supplying, power steering, side radiator fan??? Do you have any issues with those?

Lastly, if there are no solutions, I would replace the hydraulic pump with a new or rebuilt model.

Hopefully you're not giving up on RVing and will buy another, maybe newer.

DSDP Don wrote:
Hopefully a hydraulic engineer with some knowledge of RV hydraulics will post and can describe if there is some type of pressure regulator that can be adjusted or replaced.

Fingers crossed. :-)

DSDP Don wrote:
Out of curiosity, what brand of filter are you using. Is there an OEM filter available and have you tried one. The reason I ask is that some spin on filters have a built in bypass.

I've gone through a few filters. The original one was probably (frighteningly) the original. It was a Fairey Arlon FA35-25. Those aren't widely available if at all and there was no date written on it. I have started writing install date and mileage on all replaceable filters whenever I can, but I have no idea how long this filter had been in place. I've been using different cross-reference filters from the FA35-25, and currently have a WIX in place because I was able to grab 3 of them at an auto-parts store to have spares on the road.

DSDP Don wrote:
What is that pump supplying, power steering, side radiator fan??? Do you have any issues with those?

The hydraulic pump is driven off the engine with a dedicated belt. It powers steering and 2 hydraulic fans on the side radiator. No apparent problem with those though sometimes I'll hear a little whine from the steering during turning. I replaced one hydraulic fan a couple years ago and maybe (or not) the hydraulic filter was replaced by the shop at that time. I haven't looked at that expensive receipt. I may have burned the receipt in a fit of spite over the total bill. Not sure why hydraulic fans were used instead of commonly available automotive electric radiator fans. The hydraulic motors are crazy expensive, not widely available so parts have to be ordered, and require people trained or competent in hydraulics to replace. If I were going to keep this coach I'd probably replace the fans with electric motors just for reliability.

DSDP Don wrote:
Lastly, if there are no solutions, I would replace the hydraulic pump with a new or rebuilt model.

Yea, that's on my list of options. Being nearby oil fields the hydraulic shop in town does a lot of rebuilds or may have an alternate. My mechanic said he could just plumb around the filter and effectively remove it from the system but then if an overpressure situation occurs I wouldn't want to burst a line. A spin-on filter I can carry a spare (or 3-4) and replace on the side of the road. A burst hydraulic hose isn't within my capability or desire to mess with. So I'm most interested in learning how our hydraulic system are plumbed and how they regulate pressure.

DSDP Don wrote:
Hopefully you're not giving up on RVing and will buy another, maybe newer.

Well we're still youngsters (39 and 42). We bought the coach in '09 after a job loss when we knew we were moving but didn't know where. We spent the summer full-timing with our kids and driving all over California, and Texas visiting friends and family and going on job interviews. We settled in Texas and kept the motor home for long distance road trips to visit my in-laws in Mississippi every holiday and during the summer. It's a great road trip vehicle with room for the kids to not be kicking each other, toilet immediately available and even once heated up a can of soup while stopped for a 1/2 hour because the highway was blocked by an accident.

Around town we were fine with our sedans but for road trips taking the dogs and luggage and stuff we used the motor home. We had a new baby this summer and finally needed a minivan for even in-town use. With a minivan option for road trips it just doesn't make sense to keep our coach. When we reach retirement age I definitely will consider another one, but for now it'd be better used by someone else.

Verify the filter is on the return line/low pressure side of the hydraulic system.

On that age coach, someone may have replaced hoses and mis-plumbed it.

I would agree with wolfe10. In many years of working on heavy equipment, I don't recall a filter in the pressurized side of the pump. Usually it's in the return line to the tank.

Carl

dangerbird wrote:
I would agree with wolfe10. In many years of working on heavy equipment, I don't recall a filter in the pressurized side of the pump. Usually it's in the return line to the tank.
Carl

I'll have to trace the lines a bit. I had thought the pump's pressurized output went forward to the steering and the lines on the way back went through this filter before the hydraulic fans.

There is a set of filters stacked within the main reservoir at the engine door next to the roof ladder. Maybe this spin-on filter is just an extra filter for protection of the sensitive and expensive hydraulic fan motors. I could see enough to see that after the spin on filter the fluid ran to the fans and fan controllers.

I posted in the hope someone had experienced this before and hopefully could point me straight at the likely fix. As with so many things I'll keep poking but I do appreciate any and all suggestions of things to look for and try!

Not sure I understand why you would have two different filters on a hydraulic system. This is particularly true if you have the large canister with a stack of 2-3 filters. That is a LOT of filter media with very little restriction due to surface area.

Out of curiosity, check the micron rating on the large canister, stacked filters vs the spin on unit.

Now, if you actually have two separate system, one for PS and one for the fans, the two filters make perfect sense.

Only one thing blows up filters and that is excessive pressure. Not having enough information to find the schematic for your system you will either have an inline pressure bypass valve or an internal bypass in the pump. One or the other is allowing the pressure to grow until the filter blows. It could be that someone has mickey moused the system to increase pressures because of a faulty fan drive or other issue with this portion of the cooling system. The stacked filters in the reservoir may be partially clogged restricting the intake to the pump and this was "corrected" by playing with the bypass, if it is external. Pull the pump, have it checked but be sure to tell them it occurs after an extended run. Otherwise they will run it for a few minutes and possibly pronounce it good to go. If it checks out ok start looking for wires disconnected, spliced together or other obvious signs that someone did not want to spend the money to fix a previous issue in a proper manner because of cost. This could easily be something as simple as a return line restrictor, normally installed near the reservoir for noise reduction or splash control, that has become partially blocked with age. Good luck with the repair. I hope you can do this yourself because it will get very expensive to have someone else do it.
Randy

wolfe10 wrote:
Not sure I understand why you would have two different filters on a hydraulic system. This is particularly true if you have the large canister with a stack of 2-3 filters. That is a LOT of filter media with very little restriction due to surface area.

Out of curiosity, check the micron rating on the large canister, stacked filters vs the spin on unit.

Now, if you actually have two separate system, one for PS and one for the fans, the two filters make perfect sense.

Yes, my coach has the stack of filters in the canister reservoir. Will check micron ratings and call Monaco Tech Support to see if they can confirm I'm using the right filters.

randallb wrote:
Only one thing blows up filters and that is excessive pressure. Not having enough information to find the schematic for your system you will either have an inline pressure bypass valve or an internal bypass in the pump. One or the other is allowing the pressure to grow until the filter blows. It could be that someone has mickey moused the system to increase pressures because of a faulty fan drive or other issue with this portion of the cooling system. The stacked filters in the reservoir may be partially clogged restricting the intake to the pump and this was "corrected" by playing with the bypass, if it is external. Pull the pump, have it checked but be sure to tell them it occurs after an extended run. Otherwise they will run it for a few minutes and possibly pronounce it good to go. If it checks out ok start looking for wires disconnected, spliced together or other obvious signs that someone did not want to spend the money to fix a previous issue in a proper manner because of cost. This could easily be something as simple as a return line restrictor, normally installed near the reservoir for noise reduction or splash control, that has become partially blocked with age. Good luck with the repair. I hope you can do this yourself because it will get very expensive to have someone else do it.
Randy

So I know the spin-on filter is new as I've replaced it 5 times in the past year or so. I'll pull and change the filters in the canister too. Here's hoping it's that simple and cheap. :-)

My regular mechanic also suggested pulling and bench testing the pump but I will definitely let the shop know the pressure builds over 4 hours not 4 minutes! Good suggestion!

If I can get under and trace the hose route what would I look for in terms of an external bypass as opposed to a bypass built into the pump itself. Would it look like an inline check valve or would it be more of a T where it would divert extra pressurized fluid back to the reservoir?

Also, what might a "return line restrictor" look like? Would it be right at (or in?) the canister filter?

Thanks!

As tech who spent years working on CNC, industrial machines and robotics, with high pressure hydraulic systems

You have a restriction problem somewhere in the system
Or the hydraulic pressure regulator ( if one exists in your system ) is malfunctioning

When pumps fail they loose pressure, unless there is an internal regulator that is failing

Machine systems all had external regulators attached to the output of the pump, which then feed the manifolds containing the valves

So those are the two choices, restriction
Or
Failing regulator ... internal or external

E,
The return restrictor is simply a pea placed in the return line near the reservoir. You can usually see a slight bulge in the return hose.
Randy