Backhoe LW-7 backhoe foaming out the dipstick

[Bob Rooks]

Again, I'm fully supporting RonMar's precise advice here. It's also the advice I hear from local experienced hydraulic shops.

I do believe the engineers at Prince manufacturing know a little bit more about hydraulics than Mr. Casey, or your "experienced hydraulic shops."

 

[Bob Rooks]

New ZINGA. Spin-on type element. Ports 1 1/4" NPT.

SPECIFICATIONS

■Suction Line Applications 25 Micron
■25 GPM
■5 PSI bypass
■950 sq in filter area
■5 1/3" dia x 9 1/3" long

Prince calls for a suction filter for their pumps

Same as me, and I have no problems as you can see. :thumbsup:

 

[johneic]

A growling pump causes disturbance in this stream and bubbles occurs.

Your pressure seems OK though, the PRV is working. But a bit surprising, still hearing no growling and you get this foaming?

]

I hear a popping noise when I am reading 2,200 psi (The PRV doing its job) this is the growling you are talking about?

No noise is comming from the pump itself.

 

[johneic]

OK you guys, a very simple test is in order to validate my point.
John, if you will install a simple vacuum gauge on the outlet side of your suction filter (between the filter and the pump), you will know in an instant if your pump is starving/cavitating.
.

I have one on there, it is essentially the same as yours, I copied you Bob, Zinga filter, gauge looks the same too, all from Surplus Center. Only difference I see between your set up and mine is the vaccume gauge screws into the top of the filter cartridge head. My vaccume gauge reads one when it is stone cold and zero once it has been run/warmed up for a bit.

What is the test Bob?

 

[traktorz]

I hear a popping noise when I am reading 2,200 psi (The PRV doing its job) this is the growling you are talking about?

No noise is comming from the pump itself.

- Well, you got problems with foaming, so something is not working correct.
- In order to get the reading 2,200 psi, what functions are you using to view that? The boom, dipper, or the bucket? All the same?

The reason for asking is to help diagnosing where the problem occurs; At the suction filter, valve block, or the cylinders/hoses. The pump seems to work al right, since it can actually deliver the max performance ~2000 psi.

 

[traktorz]

Prince calls for a suction filter for their pumps

- Do they?
- I've only seen this recommendation with the 100 mesh suction strainer!

FILTRATION:
A 100 mesh suction strainer and a 10 micron return line filter, both sized properly for flow and both incorporating a "dirty filter" internal bypass filter are recommended. (Note: If the pump is being installed on a system where there has been a component that failed, the system should be cleaned out and new oil should be used.)

Conclusion: Get rid of the suction filter, however Prince calls for a suction strainer according to their manual pages attached here below.

 

[johneic]

- - In order to get the reading 2,200 psi, what functions are you using to view that? The boom, dipper, or the bucket? All the same?
.

Yes Sir, all top out the same

 

[Bob Rooks]

John,
Did we ever check the direction of flow on the filter head? In & out?

Suzuki and Tanaka have an alternate solution to the aeration issue.
http://www.machinerylubrication.com/Read/373/entrained-air-oil-hydraulic

There are four other LW-7's and two LW-6's that I know of with the same suction side filtration setup that are working just fine. Yours is the only one I know of that is having issues. There could also be a problem with the valve stack but I haven't run across it before.
You can temporarily remove the suction side filter and see if anything changes.

 

[J_J]

All of the Power-Trac machines have 10 micron suction filter at the input to the charge pump and I am thinking that most large hydrostatic transmission also have suction filters. You have to keep the fluid clean as possible, and you can't always expect the fluid in the tank to be clean.

So suction filters are used more than you think.

Any filter, whether suction, return or tank filter that gets clogged up is working at a disadvantage.

Of course the worst case of damage is caused by a clogged suction filter that caused damage to a high priced pump.

So what are you going to do if your next machine comes with a suction filter. Are you going to re-engineer the hyd circuit.

Foaming could be caused by suction leak, cavitation, and over worked relief valves, and possible wrong fluid.

 

[Rich Waugh]

If they have a filter as fine as 10 micron, then they must use one that is rated for a flow about ten times what the pump moves, or they're gonna be starving that pump and cavitating it in very short order. That just seems like a silly way to design a system, to me. Put the fine filter on the pressure side return line and a 25 to 100 micron on the intake if you need one. Since the system is a loop, the return line filter will do just as much cleaning as the suction filter, I'd think.