Hydraulic filter bypass

[J_J]

Guess what guys, there is none.

Disabling the bypass on the hydraulic filter, is something new to me. Apparently they have been doing this for a good while. Terry at Power-Trac verified they were doing this since they started making PT's in the early 80's. I am not so sure that someone has replaced the housing for the filter. So, I really don't know what I have, except it is a filter assembly, with a 10 micron filter. They do not have any manual for the model I have, which was built in the mid 80's. early 90.

I can see the logic, and that is to prevent any trash getting in the closed loop system, but if you don't keep up with the hours, you might jeopardize the VSP unit, and if it fails, it ain't cheap. I wished someone would tell us about these modifications. What is unique about the closed loop system in the PT's, is that the pump sucks fluid from the wheel motor output, and the charge pump replenishes whatever is necessary to maintain the correct volume.

On the filter housing gage, I believe, that it has to be a vacuum reading/indicator, as there is no pressure , except atmospheric. A vacuum gage in the pump input line will read zero with the pump not running.

 

[ponytug]

JJ-
You would want a differential pressure gauge to keep track of the vacuum on the filter. I'd consider shelling out the extra bucks for one that recorded maximum pressure drop.

PT is pretty open about the lack of bypass; Terry emphasized to me that the lack of bypass was to keep the charge pump from getting dirt, because the drive circuit recirculates the oil until it blows by the motors into the case drain. (For those machines that have case drains.)

I have it filed under reason #345 why you want to service your PT in cleaner than clean conditions. (Terry's phrase was "heart bypass surgery clean".)

You can get replacement oil filter housings that incorporate a pressure gauge, e.g. mcmaster-carr, if you want.

All the best,

Peter

 

[Gravy]

FWIW, I just spent some time with Terry and Keith today. We talked about a bunch of stuff - too many little things to try to detail. They gave me their best advice instead of just blowing smoke to get me to throw money at them.

That was the best part of my day. (Well, at least until dinnertime with the fresh batch of smashed taters and roast beast!) ((anything after that is subject to strict privacy standards!))

 

[Bob999]

I installed a simple vacuum gage on the hydraulic filter housing. Even in the summer a "cold" start up will register high vacuum--20" + but the vacuum will fall as the oil warms and on my machine registers 5" or so at full throttle when the oil has warmed.

So I see the disabling of the bypass as a reasonable trade off--to avoid the introduction of dirt during cold start up that would continue to circulate as being preferable to some cavitation during cold start up.

 

[J_J]

Bob,

Did your filter housing have a place for the gage, or is that a different filer housing. I believe Terry aid that they did not put filter housing with gage ports, so if anybody has one, it may be after market, and not modified, to plug the bypass orifice.

Here is a picture of my filter, but I don't know if it is original.

 

[Bob999]

Bob,

Did your filter housing have a place for the gage, or is that a different filer housing. I believe Terry aid that they did not put filter housing with gage ports, so if anybody has one, it may be after market, and not modified, to plug the bypass orifice.

Here is a picture of my filter, but I don't know if it is original.

Yes the OEM filter housing had a port for a gage

 

[ponytug]

20" of vacuum on a summer start is a scary thought.

Maybe I will go for that magnetic heater for the oil...

Did you have to drill your filter assembly out to install this? Mine doesn't have a gauge port.

Thanks for sharing this.

All the best,

Peter

I installed a simple vacuum gage on the hydraulic filter housing. Even in the summer a "cold" start up will register high vacuum--20" + but the vacuum will fall as the oil warms and on my machine registers 5" or so at full throttle when the oil has warmed.

So I see the disabling of the bypass as a reasonable trade off--to avoid the introduction of dirt during cold start up that would continue to circulate as being preferable to some cavitation during cold start up.

 

[J_J]

Yes the OEM filter housing had a port for a gage

Did you purchase your PT new from PT, and as far as you know, Pt installed that filter housing?

I guess you could install a tee and a port for a vacuum gage. I can't remember the in of mercury that cavitation starts, And that isn't the problem, It is the effect of the collapsing or bursting of the bubbles that will cause erosion, even on some of the hardest metals. That makes me curious about those aluminum body on some hyd pumps.

 

[Bob999]

Did you have to drill your filter assembly out to install this? Mine doesn't have a gauge port.

Thanks for sharing this.

All the best,

Peter

No drilling required. There was a threaded plug in the port and installation only required removing the plug and screwing the gage into the port.

I think I recall that Sedgewood also installed a vacuum gage.

I purchased my PT new from the factory.

 

[dfkrug]

I have it filed under reason #345 why you want to service your PT in cleaner than clean conditions. (Terry's phrase was "heart bypass surgery clean".)

I, too, am amazed there is no bypass, and the designer allows 20psi or
more of vacuum. It seems to me that warmup is critical for these machines.
I agree on the cleanliness aspect of these kinds of hyd systems. Since
you are local to me, Peter, maybe I will get to see one of these rare PT
beasts some day.....

(JJ, its good you went back to the ZZ-top beard. Looks great!)