closed loop...really?

[J_J]

Army - FM 5-499 - Hydraulics

Thanks, That link worked, and the explanation of what happens to the fluid from the charge pump was the same as the Eaton pump, recirculating the fluid back to the input of the VSP, with some going to the case of the pump.. I am thinking that the fluid sent through the pump case is to help to cool the pump. I think the PT has minimum cooling, and should be improved. A 20 gal hydraulic tank too hot to touch is holding a lot of heat.

 

[Bob999]

The 1850 I have (I assume 1845 and I think the 1445) has a second filter. The primary is the big one from the tank to the Wheel Motor Inflow pump. This is the biggest mystery to me. Change this filter every 50 hours but it filters very little, right? There is no return back to the tank on this system. It is only providing filtered oil at a limited rate to the wheel motors, right? The thing is that if this is to a closed loop system, why such big supply hose? 1" from the tank to a 3/4" to the wheel motors. But like I said I do not see any return line, although there is a mystery hose hanging off the back of the pump so maybe that is it.

Carl,

This is another area where PT has built different units with differing technical details. My 1845 (purchased new from PT in 2003) has only one filter--the large hydraulic filter between the sump and the intake side of the charge pump. The charge pump is continuously pumping fluid to the intake of the variable displacement pump (the two pumps are located in the same case). The variable displacement pump needs a positive intake pressure to work but typically requires very little new (makeup)fluid because fluid is returned from the wheel motors to the variable displacement pump intake (it is this return that is the basis for the statements that the drive system is "closed loop"). The excess fluid (excess in the sense that it is a larger amount than necessary for makeup for the wheel motors)from the charge pump flows through the hydraulic oil cooler and back to the sump. I read somewhere, but cannot document, that the charge pump delivers 2-5 gallons per minute. As to your question about the big hose on the intake and output side of the hydraulic filter see my post above--it is about maintaining adequate flow with small differential pressure.

 

[marrt]

Woodlandfarms, when you get a chance, could you post a picture of the high pressure filter. I think you posted it before...but, as usual, I can't find it. To my knowledge, your PT is the only model I've heard of that has a high pressure filter from the factory (unless someone added it later). My 1845 only has one filter, but I'd like to add a high pressure filter. It would be nice to see where PT choose to put it.

 

[woodlandfarms]

Here is a picture of the filter.

On the top it says Schoeder F-11 but I cannot find any record of it on the net. There are some other numbers on the filter container but I have to take it off to read it. It takes a Schroeder N-25 filter, again, hard to find and grossly overpriced by PT. I find them now online for $8 per filter and PT charges me at least $25.

This all said... How it is run is there are two lines out of the "front" pump, one is PTO, one is steering and lift. They go into a aluminum block under the fuel tank left side that has a solenoid and bypass valves. The solenoid is for the PTO and the oil dumps back into the tank or into the system. So, from the Lift Tilt outlet on the PTO block it goes up the the filter feeding the RIGHT side of the filter in the photo, the outlet is on the LEFT side. From the outlet it goes down to the Accumulator valve located just behind the Left rear wheel. 1/2 inch hose I think.

This filter has a quality meter on the top which I do not think works.

 

[J_J]

Here is a picture of the filter.

On the top it says Schoeder F-11 but I cannot find any record of it on the net. There are some other numbers on the filter container but I have to take it off to read it. It takes a Schroeder N-25 filter, again, hard to find and grossly overpriced by PT. I find them now online for $8 per filter and PT charges me at least $25.

This all said... How it is run is there are two lines out of the "front" pump, one is PTO, one is steering and lift. They go into a aluminum block under the fuel tank left side that has a solenoid and bypass valves. The solenoid is for the PTO and the oil dumps back into the tank or into the system. So, from the Lift Tilt outlet on the PTO block it goes up the the filter feeding the RIGHT side of the filter in the photo, the outlet is on the LEFT side. From the outlet it goes down to the Accumulator valve located just behind the Left rear wheel. 1/2 inch hose I think.

This filter has a quality meter on the top which I do not think works.

Schroeder Hydraulic Filters

Phone number on this page

http://filters-gbs.com/cgi-bin/hydraulic/list.cgi?p=SCHROEDER

http://www.schroederindustries.com/products/hf-filters-high-pressure-filters.asp

 

[woodlandfarms]

And here is one more.

Thanks JJ for the info. It is just that I have not found my specific type of filter holder. Must be an older model. I have found a few filter places to buy from, not sure of reliablilty.

 

[Bob999]

So, from the Lift Tilt outlet on the PTO block it goes up the the filter feeding the RIGHT side of the filter in the photo, the outlet is on the LEFT side. From the outlet it goes down to the Accumulator valve located just behind the Left rear wheel. 1/2 inch hose I think.

Carl,

From your description of the circuit it sounds like this filter only filters oil to the accumulator. On my 1845 the accumulator is supplied from the variable displacement pump--which gets filtered oil via the charge pump.

My guess is that the accumulator is very sensitive to foreign matter in the oil and the filter is installed in your PT because the accumulator is supplied with oil from the lift tilt circuit which comes directly from the sump without filtering. For those of use with the accumulator on the drive circuit the additional filter is not required. Additionally, the high pressure filter would filter very little oil if it is only connected to the accumulator.

One thing puzzles me however--the annual filter change. The amount of fluid moving into the accumulator is quite small and at high pressure. It is hard to imagine that it would load up and require frequent replacement.

Your filter looks like the Schroeder NF30.

 

[ponytug]

Just to add my $0.02, my 2007 1445 has only one filter.

David, you asked about oil flow in neutral. The great thing about the swash plate variable pumps is that they do almost no work in neutral, since the pistons are set at zero volume. The charge pump oil bathes the plate, and provides the necessary cooling. The downside, in my opinion, is that the swashplate variable pumps have many, many more parts and wear surfaces, compared to a standard displacement pump, such as the PTO pump.

The PT design appears to try to protect the most expensive pump with the least parasitic filter loads. If you aren't horsepower limited in your usage, adding additional return line filters, or a PTO bypass filter, would provide more filtering, which wouldn't hurt, provided that they were changed before much of a pressure differential develops. Of course, the filters do add additional loads on the engine, especially cold, and are going to cause the the tractor to run hotter when it is warm...

Carl, I am probably missing something, but why did you want to have a flow meter in the system?

All the best,

Peter

 

[woodlandfarms]

So, I am still learning. What is the Variable Displacement pump? On my PT I have 3 pumps (excluding the Accumulator / charging device which Terry said is kind of a pump). One is the tram pump, one is the PTO and one is the steering, lift, tilt brakes pump. The PTO and Lift pump are one unit, although two pumps stacked to look and be sold as one unit.

From initial appearances it does look like this is the only source of oil for the accumulator. You said it does not take much oil. If that is the case then quite frankly I am really perplexed in my filtering system. I guess I should put some sort of 18GPM, 3000 PSI filter on the PTO as it turns all the time (just dumping back into the tank if not in use). Wonder if such a bad boy exists.

As for the flow meter, this goes to my complete ignorance of the PT system. I do want to put pressure readers throughout, but I thought a flow meter, with a thermometer, would give me some indications of system health as well.

Carl

 

[ponytug]

Carl,

Sorry to have confused you and anyone else. The tram pump, aka VSP, aka variable volume swashplate pump, is the primary pump driving the wheel motors on the tractor. The variable volume swashplate enables stop, slow, fast, forward and reverse. As I wrote, it has lots of advantages, but tolerance of dirt particles isn't one of them.

There are other kinds of variable volume pumps for different purposes. e.g. if a standard piston pump has a spring added between the piston and the crank, the displace is reduced as the load increases, enabling a more constant load on the motor. It is often used in situations where the load is fluctuating, e.g. log splitters.

Based on comments at TBN, I think that PT may have had issues with the seals in the accumulators over the years. Your filter may have been an attempt to see if filtering would have an impact on the seal/accumulator wear.

Personally, I think that until you get all of your hoses replaced, I wouldn't dare put a flow meter in any circuit that was not directly filtered. I have had some spectacular flow meter failures when a piece of debris gets stuck. In general, I think that know what the pressure and temperature is at various points the system is probably more informative about your system health and performance.

A trick that I have used in other situations is to use a hose clamp to hold a thermocouple in good thermal contact with an item of interest, and then insulating the area with a bit of hose insulation. It doesn't make for a fast responding temperature, but it usually is pretty accurate. It often beats trying to find a 4000psi JIC-3.19.45-SN-9Q class K thermocouple hydraulic fitting...

Omega sells a variety of tthermocouple products.... Not cheap, but.. Their CN606 will monitor six thermocouples and set an alarm when any of them are out of bounds.

All the best,

Peter