Hydraulic filtration

Bob999 · Aug 21, 2003

Mossroad and Smartguyz:

My understanding is that the PTO pump and the Auxiliary pump are always pumping--thus the phenemon you report. Also the variable displacement pump is always spinning--all of the pumps are driven by the same shaft--but it does not pump fluid in "neutral".

In the case of the PTO pump there is an electrically actuated switch that controls whether the pump simply circulates back to the reservoir, thereby consuming little power, or flows to the attachment. PT cautions against actuating the PTO switch without having an attachment because if there is no attachment then pressure quickly builds up and the safety valve is actuated.

The auxiliary pump is "always on"--that is why you can steer or lift the arms at any time the motor is running.

But, I continue to believe, the variable displacement pump is not pumping any fluid when the treadle is centered.

MossRoad · Aug 21, 2003

OK, here's a way too cool link to how a variable volume pump works.
http://science.howstuffworks.com/backhoe-loader8.htm It even has a movie of a cutaway pump in action. When the swash plate is even, no fluid is pumping. So what is heating up the hydraulic fluid while idling? Hmmm...

MossRoad · Aug 21, 2003

Also, I just posted this link in the related topics forum. It describes how skid steers work. There is some good information for everyone in there. Check it out.

Bob999 · Aug 21, 2003

this means that the temp sensor has been activated because of hitting the trip point for the temperature sensor. So, if it is not being moved under pressure, where is it going? 

I think that the fluid flow for the cooler circuit is taken from either the PTO or Auxiliary pump circuit. I do not believe that it is taken from the wheel drive circuit (variable displacement pump). I went to my PT manual to find the answer and found that no diagram in my book includes the cooler!!!! I do have what appears to be a complete diagram of the wheel motor circuit and the cooler is not shown.

Perhaps the manual for the 425 does include this.

Sedgewood · Aug 22, 2003

Bob999: I think that the fluid flow for the cooler circuit is taken from either the PTO or Auxiliary pump circuit. I do not believe that it is taken from the wheel drive circuit (variable displacement pump). Actually it is taken from the variable displacement pump here.

 I went to my PT manual to find the answer and found that no diagram in my book includes the cooler!!!! Sounds like you might be missing a page of pretty lousy drawings - it's on drawing H077x2, Power Take-Off Circuit, even though it's not connected to the PTO! - go figger. (BTW, for the curious, the cooler fan thermostat is attached to the aluminum block of the cooler bypass valve here - well sort of - it doesn't actually touch the block - it stands off about an eighth of an inch for some reason) Now that I've become so intimate with the plumbing of my 1845 I'm going to try and draw up something a bit easier to follow (and correct a few mistakes while I'm at it). I'll post the results on my PT wiki when I get it done.

Up to his ears in hoses,
Sedgewood

Bob999 · Aug 22, 2003

Sounds like you might be missing a page of pretty lousy drawings 

I double checked--no page H077x2--but it is listed in the index!!

Thanks for the correct information.

I had previously found that the quick attach circuit is not shown in my manual and asked Terry about it. He confirmed it was not there but iqnored my request for a copy of it.

Taking the cooling flow from the variable volume pump means (I think) that there is no flow in this circuit when the machine is sitting still. If that is true then there is a potential for significant heat build up in the hydraulic oil if the unit is left sitting, but running, for a significnat period of time. Of course on the 1845 you have to be sitting in the seat, or defeat the seat switch, to have the machine running when you are not in the seat.

Sedgewood · Aug 22, 2003

I put together a quick hydraulic cooler circuit and posted it here. it's pretty rudimentary and I'll improve on it when I get some time.

I double checked--no page H077x2--but it is listed in the index!! 

I'd be happy to scan any pages you're missing and email them to you.

Taking the cooling flow from the variable volume pump means (I think) that there is no flow in this circuit when the machine is sitting still. If that is true then there is a potential for significant heat build up in the hydraulic oil if the unit is left sitting, but running, for a significnat period of time

I'm don't know how the oil flows through the variable volume pump but it's possible there is a continuous flow to the cooler from there.

Of course on the 1845 you have to be sitting in the seat, or defeat the seat switch, to have the machine running when you are not in the seat. 

Some of us without tilt seats don't have that little problem - we just get to hang on tighter on slopes /forums/images/graemlins/tongue.gif

Sedgewood

duane · Aug 25, 2003

Bob999,

The PTs actually have 4 pumps. The Tandem PTO/lift steering pump, and the variable volume pump with suction charge pump. The charge pump provides suction flow to the variable volume pump. (when you change your hydraulic filter, the jumper line to the reservoir is discharging the charge pump discharge to purge any air) The charge pump is always pumping oil. In a non tredle position, the charge pump recircs all oil flow back through the oil cooler to the reservoir.

Duane

MossRoad · Aug 25, 2003

The PTs actually have 4 pumps. The Tandem PTO/lift steering pump, and the variable volume pump with suction charge pump. The charge pump provides suction flow to the variable volume pump. (when you change your hydraulic filter, the jumper line to the reservoir is discharging the charge pump discharge to purge any air) The charge pump is always pumping oil. In a non tredle position, the charge pump recircs all oil flow back through the oil cooler to the reservoir. 
Duane's Da Man!!! Thanks for the explaination /forums/images/graemlins/laugh.gif