Backhoe LW-7 backhoe foaming out the dipstick

[johneic]

Sounds like air getting into the system.

Chris

I think so...

 

[RonMar]

What filter are you using? If it is a "filter" that is most likely your problem. Strictly speaking, filters do not belong on the suction side of a hydraulic circuit. They restrict the flow too much, and hydraulic pumps push better than they pull. Now they do make spin on metal mesh strainer cartridges that are specifically for suction applications, and are labeled as such. Quick indicator is the micron rating. 10-20 micron, it is a type filter designed for fluid to be pushed thru it, not pulled and is supposed to be on the return side of the system just before the reservoir(pressurized flow, but not system pressure). A suction side strainer will be around 150 micron or so... Filter restriction could be causing air to sucked past the filter seal or past the shaft seals in the pump itself, or at a fitting. At any rate suction restrictions are hard on the pump...

If this is the case, you need to take that filter boss out of the circuit on the suction side, and install it in the return line just before the fluid flows back into the tank. This will keep any contaminant from the system from entering the tank. If you are careful with what you put in the tank, itnshould work great. That is where I put my filter...

 

[Bob Rooks]

Strictly speaking, filters do not belong on the suction side of a hydraulic circuit. They restrict the flow too much, and hydraulic pumps push better than they pull.

Puhleeze! I beg to differ. Suction side filtering is very common and highly desireable, as is pressure side filtering and return line filtering.
The reason you don't see the other filter types on this equipment is simple - cost.

These are representative of filter manufacturers that service all facets of hydraulics.

Industrial Manufacturing

Donaldson Company, Inc. - Global Home Page

 

[Diamondpilot]

I also agree that the filter on the suction side is asking for issues. I know you can get away with it but I would much rather have it on the return side.

A screen on the suction side is ok but a filter can lead to cavitation issues and pump erosion.

Yes, Bob Rooks know's his stuff but looking at the many many hydraulic systems I have been around 99% have the filters on the return side. Just sayin.

Chris

 

[RonMar]

Puhleeze! I beg to differ. Suction side filtering is very common and highly desireable, as is pressure side filtering and return line filtering.
The reason you don't see the other filter types on this equipment is simple - cost.

These are representative of filter manufacturers that service all facets of hydraulics.

Industrial Manufacturing

Donaldson Company, Inc. - Global Home Page

Yep, they do make them, but in addition to material costs, they also require more engineering to not do more harm than good. You can put a filter there, but it needs to be proper for the application.

They are not all that common in my experience... What I am used to seeing is a wire mesh strainer at the tank fitting leading to pump suction and a return line filter on the line back into the reservoir... Log splitter 101

From the OP's description, he may also still have the wire mesh strainer inside the tank?

Guy having BH troubles foaming, jerky, weak ect. Sounds like air intrusion on suction side to me. Oh, modified suction side and cartridge filter added? In this case I think 2+2 will indeed add up to 4...

 

[traktorz]

... I removed the stock suction banjo fitting on the tank and had a welder enlarge it and weld in a 90 degree 1.25 inch elbow, put a 25 gpm filter inline with a vaccume gauge that reads zero when normal running and one at stone cold.

No growling from pump
...
reservoar is not too low, about an inch from the top of tank, less as this went on.

I am not sure how I can do this, please explain, look in the tank with a mirror while running only one function?

I have to write more to get this to post, I have a pressure gauge on the 3/4 hose I put on the pump, it sticks at 2,200lbs

I can look through the fill hole of our oil reservoar and see the return oil stream above the oil surface. 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?

Remove the filter from the suction line

But, it seems we have a somewhat different setup; I have a tank return filter, while you have a suction filter.
(See my illustrative sketch, however with some text in swedish.)
However, there is a suction line strainer (mesh filter in a plastic housing) in our hydraulic reservoar. I've checked/replaced it once, after a long season of digging, and it still was in mint conditions.

My recommendation therefore is simply to remove your suction line spin-on filter & holder, since I think it's causing more pain than gain. If you're going to add any filtering at all, do that on the return line only.

 

[traktorz]

What filter are you using? If it is a "filter" that is most likely your problem. Strictly speaking, filters do not belong on the suction side of a hydraulic circuit.

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


Ref:

• The Negative Effects of Suction Line Filtration
• Determining Hydraulic Fluid Viscosity Requirements
• How to Select the Right Hydraulic Oil
• Hydraulic Filter, Hydraulic Filters
• Hydraulic Filter, Hydraulic Filters

 

[Bob Rooks]

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 had an identical setup on my dozer with the Prince pump and a LW-6 backhoe (which I replaced with a LiTW BH7600 backhoe and still use the same suction side setup). See pics. (Engine speed was ~1,200 r/m with ~ 50 degree F cold AW ISO 32/46/68 multi-grade hydraulic oil.) It should also be noted that I'm using a 25 micron suction filter that has a 25 gpm rating - on a 7 gpm pump that's only putting out ~5.5 gpm. I'm also a big fan of Machinery Lubrication, plus Facilities Engineering, etc. In Brendan Casey's article he demonstrated extreme worst case scenarios, and never once concluded that suction side filtering was a bad thing. The article is seven years old, and I believe there have been several SAE white papers on the subject since.

 

[johneic]

What filter are you using?

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

 

[johneic]

From the OP's description, he may also still have the wire mesh strainer inside the tank?

I removed the wire mesh strainer in the tank, it only had about a 1/4 inch opening on it, I wanted to feed the pump all the oil it wanted and opened up the outlet of the tank to 1.25 inches