Oil Recirculation in closed loop system

[woodlandfarms]

So I took my steering cylinders apart this week. Put a clear bucket underneath to capture the oil. It came out kind a dark. Was surprised at how dark it was. I took a syringe and pulled from the tank and the tank was a lot clearer.

I am just wondering on the PT as many of the systems look to me to be closed looped if they should not be drained and allowed to refill from the tank every now and then (This is the steering circuit, but I am thinking the wheel motor circuit as well).

 

[J_J]

The wheel motor circuit is a closed loop hyd circuit, and recirculates the oil until some leak or bypasses the wheel motor themselves.

I have case drains in my wheel motors, and that fluid is sent back to the cooler and tank.

The tram pump also makes up any fluid lost for any reason using the charge pump.

Some of the fluid is flushed through the pump case and back to the cooler and tank.

Those wheel motors that have no case drains, may keep the same fluid for a long time.

The fluid in the closed loop is not filtered except when the charge pump is replenishing the fluid.

If anything comes apart in the wheel motor circuit, you have all the hyd motors, pump and hoses to clean.

I only have the one 10 micron suction filter in the closed loop circuit on my machine, a PT-1445.

Some of you could go return line filters, or even high pressure filters in each circuit.

Someone had the thought that if everything in the tank was clean, everything that uses fluid would have clean fluid.

The charge pump, when replenishing the fluid is pumping at about 10% of main pump flow.

You could probably put a tee in the wheel motor circuit and feed some of the wheel motor fluid to tank, and the charge pump would replenish the closed loop with fresh filtered fluid.

 

[MossRoad]

So I took my steering cylinders apart this week. Put a clear bucket underneath to capture the oil. It came out kind a dark. Was surprised at how dark it was. I took a syringe and pulled from the tank and the tank was a lot clearer.

I am just wondering on the PT as many of the systems look to me to be closed looped if they should not be drained and allowed to refill from the tank every now and then (This is the steering circuit, but I am thinking the wheel motor circuit as well).

Yeah, unless your cylinders leak past the seals, and even if they do, you're probably never going to get that fluid rotated out of the steering circuit. It just pushes and pulls, but doesn't pass trough. The good news I guess is that the nasty oil in the cylinders will probably stay there forever and not contaminate the rest of the system.

 

[KentT]

JJ,

Since the wheel motors are reversible, and frequently used in reverse, how could you tee in a return to tank line into a line that becomes a high-pressure line and not a return line, based on treadle position?

 

[MossRoad]

JJ,

Since the wheel motors are reversible, and frequently used in reverse, how could you tee in a return to tank line into a line that becomes a high-pressure line and not a return line, based on treadle position?

I think you'd lose some power at the wheels.

 

[SpringHollow]

I always thought the joystick valve had a return to the tank and you would be getting the cylinders purged with use. Shows what I know.

Ken

 

[MossRoad]

I always thought the joystick valve had a return to the tank and you would be getting the cylinders purged with use. Shows what I know.

Ken

- Small PTO pump section supplies the steering valve.
- The steering valve's power beyond port powers the AUX PTO and FEL valve bank.
- The AUX PTO and FEL valve bank returns the fluid to the tank.
- The knee bone connected to the thigh bone...

 

[J_J]

I think you'd lose some power at the wheels.

I did not mean for anyone to leave the tee valve open to tank.


That valve would be to add a supply of filtered oil to the closed loop.

He said his fluid was almost black, meaning the fluid had been recirculating in the loop a long time

The fluid could have been burnt or well used with anything in it.

The fluid is only filtered by the charged pump when providing makeup fluid, and pump flushing.

 

[MossRoad]

OK, gotcha.

 

[Raw Dodge]

Most closed loop systems do leak about a pint to quart an hour so the whole system is filtered just slower, and trash will circulate, which is why high pressure loop filtering is required anytime the closed loop is opened. The steering cylinders will not leak unless the seals are bad and they will keep circulating the same fluid, and the fluid gets bad after a while...

 

[ponytug]

Is it really this bad? I don't think so, but YMMV.

1) go look at your hoses and the volume of your cylinders
2) cycling your cylinders will move some oil in/out
3) As long as some oil moves in/out, the oil will turn over in the cylinders.

On my machine, the steering and the Q/A lock are both at the end of a long circuit, but the Q/A gets switched out and flushed on some of the attachments, and at least on my 1445, the volume of the hoses from the steering wheel to the cylinders is a lot smaller than the volume of the cylinder, so it will flush.

Just my $0.02.

All the best,

Peter

P.S. I agree the steering cylinders do sit down in lots of wet stuff, but even that shouldn't be enough. Worst case, they are sealed, cool off in the rain and pull a full vacuum. However, even a full vacuum is only -14.5psi, which is a long cry from the 3000psi at WOT. If your seals are leaking in a little with 14.5psi of pressure difference, you have a much bigger problem when operating.

P.P.S. That's different that Woodlandfarm's issue of an internal seal broken or bypassing, when the oil is going from high to low and flowing back to the tank.

P.P.P.S. To RawDodge's point, according to the factory (Terry) the PT hydraulics are designed to leak at the valve, not the cylinder, so there is minimal leakage from the circuit through the cylinder seals by design.

Most closed loop systems do leak about a pint to quart an hour so the whole system is filtered just slower, and trash will circulate, which is why high pressure loop filtering is required anytime the closed loop is opened. The steering cylinders will not leak unless the seals are bad and they will keep circulating the same fluid, and the fluid gets bad after a while...

 

[Raw Dodge]

Sorry I referring to wheel motors in a closed loop system,they all leak,it's normal to leak a little,fluid is usually returned via a case drain or the leakage just pours into the transmission the motor is bolted to,and returns via the transmission cases pickup tube to the pump..as for hydraulic cylinders they only leak when there's a problem lol...and I wouldn't worry about the fluid trapped in there ,although on my snow plows I do remove the hoses and get that fluid out especially the older plows that used packing for the seals,the fluid gets lots of packing dust in it...

 

[J_J]

I have to disagree about Terry's statement about leaky valve.

Who in their right mind would search the world for a company that produces a valves spool with the highest leakage rate.

It just isn't logical. I can understand for selecting cheap product.

Did anyone see a statement like that in their manual.

We are proud to announce that we have the most leaky valve spool in the industry. You can count on us for the best leaky valve anywhere.

We guarantee that our valves will provide the most leakage anytime, anywhere.

You want a valve spool to hold the pressure or run a motor or cyl with out leakage.

Safety would be a big concern.

 

[ponytug]

This is playing telephone, but as I recall, my discussion with Terry came up around a circuit in my FEL that was leaking down excessively at the time. Terry suggested removing the plastic check valve and looking for debris. I did, and did not observe any debris, but on reassembly, the excessive leak down was fixed.

My recollection of Terry's comment was to the effect that by design one had to either engineer in pressure relief to the circuit, or select a valve block that a small amount of bleed to ensure that the cylinder circuits didn't overpressure, causing external leakage/damage. They had selected a valve block that did bleed to keep the pressures in the FEL from being excessively high.

There is always the possibility that I did not understand what Terry said to me, or that my memory is flawed.

All the best,

Peter

 

[woodlandfarms]

So here is the diagram I was given. The thing is I don't see really any place for the oil to return on the steering pumps.

I don't feel sitting in the dirt has any real effect on the quality of the oil. But IMO it really looks like they have no way of getting fresh oil without a deliberate draining.

 

[J_J]

On my 1445, I have an Eaton pump for the drive.

The charge pump is pumping continuously, supplying make up oil and flushing the pump case.

So if the main pump is 20 GPM, the charge pump is about 2 GPM.

The charge pump usually pumps about 10 % of pump flow.

Charge pressure is around 400 to 500 psi.

The flushing fluid and wheel motor leakage is then combined and fed back to the radiator fluid and then to tank.

So the fluid coming in to the drive pump is the one source being filtered, but over time, all the fluid will be filtered.

Their theory is that if the tank fluid is clean, the the other pups do not need another filter.

You could however, install return filters in each circuit at about 10 microns with gauge.

 

[MossRoad]

So here is the diagram I was given. The thing is I don't see really any place for the oil to return on the steering pumps.

I don't feel sitting in the dirt has any real effect on the quality of the oil. But IMO it really looks like they have no way of getting fresh oil without a deliberate draining.

The engine turns the aux pto pump.
The aux pto pump feeds the steering valve.
There is a power beyond port on the steering valve.
The power beyond port feeds the FEL/aux pto valve.
The oil flows out of the FEL/aux pto valve back to the tank.

Is that the path you're looking for?

 

[MossRoad]

What that diagram does not show is that item #2 (the RPS valve) is one unit. That diagram shows the front and the back of the valve separated, but does not indicate that it is really one unit. Look at it. Its a mirror image so I'm assuming that's the front and back of the same valve body.

 

[SpringHollow]

If the oil flows from the valve to the tank like I had thought, then the oil in the cylinder should look the same as the oil in the tank? If it returns to the pump intake and not the tank, then the loop could look much different than the tank. B

Ken

 

[MossRoad]

If the oil flows from the valve to the tank like I had thought, then the oil in the cylinder should look the same as the oil in the tank? If it returns to the pump intake and not the tank, then the loop could look much different than the tank. B

Ken

Nope. The oil in the cylinder is rarely, if ever, exchanged, unless it slips past the seals in the cylinder. It just gets pushed down the 'out' hose a ways as the cylinder extends, and sucked back in as it retracts. Same for the other side of the cylinder.