Variable speed transmission

[J_J]

I was trying to work out the math, but could not get a logical conclusion. I think I would first tee in a 3000 psi gage and connect the hoses together and look at the pressure at max rpm. If it is very low, I would then try the filter. If it works, that would be a great idea.

 

[J_J]

Looking through my hydraulic CD, and some books, I have come to the conclusion that the system used on the PT is an open loop system. In this circuit, the fluid goes from the tank, through the suction filter to the pump, through the motors and back to tank, It also uses mechanical controls to control the output of the pump.

 

[J_J]

Just a thought if you haven't tested the PTO filter yet. Take the output of the filter and run it into a clean bucket in case you blow the elements out of that filter. That way you won't put trash into the tank. 8 gpm coming out of a 3/8 hose comes out mighty fast..

 

[KentT]

</font><font color="blue" class="small">( Just a thought if you haven't tested the PTO filter yet. Take the output of the filter and run it into a clean bucket in case you blow the elements out of that filter. That way you won't put trash into the tank. 8 gpm coming out of a 3/8 hose comes out mighty fast.. )</font>
Wouldn't that risk cavitating the pump when you empty the tank?

 

[J_J]

You don't want to run it that long, just enough to see if the filter stays intact. If you get bits of filter material in the tank, it will take a while to get it all out, in the mean time, the other pumps are sucking that trash and sending it through the complete system. The variable speed pump filter will filter what it needs. Lift/steering , and PTO will just recirculating trash. On my 1445, I can control the PTO flow from low to high. I think the 425 is full on when the solenoid is switched on. Keep this in mind, you only have pressure when there is resistance to the flow.

 

[Spiffy]

That would be a very easy way to prevent a disaster, and would work just fine if you don't have a gauge handy.

However, if that's a 30GPM return filter, I wouldn't be worried at all; a 100psi gauge in line (or mounted on the filter, if ports are provided) would be a precaution; actually, I'd probably mount a gauge just for curiousity sake more than concerns with the filter.

I think as mentioned earlier, if you're satisfied with the results, no reason you couldn't leave it hooked up even when mowing etc (just be sure to use the return side not the pressure side!).

I may have to make myself one of those if I don't get around to a permanently mounted version anytime soon. /forums/images/graemlins/cool.gif

 

[Gravy]

I did manage to try it out on Sunday afternoon. It wasn't a total failure, but it wasn't a great success, either.

I plugged the filter assembly as a closed loop into the main PTO circuit, oil hot, engine idling. I turned on the PTO and the filter inlet pressure went to 25psi. I slightly increased the engine speed and the pressure went over 30psi, which is the limit of the gauge.

I then removed the quick-disconnect from the filter return hose and stuck the end of the hose into the tank fill port to make an open loop. This gave me 15psi at idle. Again, the pressure rose very quickly with increased engine speed.
I suspect that much of the pressure comes from restrictions in the plumbing. Replacing the 1/2" outlet hose with a 3/4" hose might help further, if it's actually needed. If I go that route, I will make up an adapter to go in place of the filler cap in order to secure the hose and keep crud from falling into the tank.

The filter is rated for a maximum pressure of 125 psi, with a bypass valve that should open when the pressure drop across the filter is 25psi. From what I can tell, filter element replacement is recommended at a pressure drop of 15psi or so.

The filter housing only has drilled and tapped gauge ports on the inlet side, so I have no idea what the actual pressure drop across the element is at present. It does have a boss for a gauge on the outlet side. I think my next step will be to drill & tap that boss and add a second gauge. Then I should be able to monitor both overall pressure and pressure drop.

I'm hoping that I will find that my original closed-loop configuration will turn out to work acceptably, since it's more compact, simpler and easier to connect without introducing contamninants to the system. I doubt that it will be practical to use it inline with working implements at full throttle due to the potential for pressure spikes. I suspect that setup would require either a larger return line and tank fitting, or a considerably higher pressure (and cost) filter.

I'll try to get the second gauge installed by the end of this weekend and report the results.

Gravy

 

[Spiffy]

Thanks for the update!

If that setup is rated for 30GPM return line filtration, something doesn't seem right. The 1/2" hose may cause a little backpressure but should be fine; I think PT's are 3/8". Maybe your fitting is too restrictive, but that doesn't seem likely.

The outlet gauge should really tell if the filter is the problem, but assuming the rating is right and the fittings aren't too restrictive:
I next have to wonder if it didn't litterally plug up after the first 10 seconds. Your oil has never been filtered finer than 10micron. Perhaps, try it with a 10 micron; if that works at full throttle, I'd go back to the 3, realizing it may take several sessions before you don't have to change the 3micron after each (each one should allow you to increase the time &/or throttle until it runs fine at full throttle).

If that does porve correct, I'd say contaminant levels are quite pronounced; and we all should be concerned. While 1micron might be overkill (about 1/100 the thickness of paper), I really think capturing the 3micron particles would be money well spent [in added longevity], even if it does take several filters before it can run continously. Also, I'd be pretty sure that it will more than double the life of the 10micron filter.

Looking forward to "take 2" /forums/images/graemlins/cool.gif

 

[Spiffy]

One more thing: any chance you can get a 100 psi gauge for the inlet side and use the 25 on the exit?

Goodluck!

 

[Gravy]

I'm hoping to round up a couple of matching gauges in the 100 to 160 psi range to use for further testing this weekend (McMaster/Carr to the rescue!). I suspect that the backpressure is due to the frictional losses in the rather long return hose and the restrictions in the various fittings along the way back to the tank.

Since I just recently changed the hydraulic oil, switching to Castrol 5W50 synthetic (it was on sale at NAPA for about $1.80/qt) I doubt that it's a severe contamination issue. Even at idle, the volume of oil flowing out of the return hose was substantial, so I wouldn't be at all surprised to find that most of the pressure drop is due to frictional losses in the plumbing.

If things go well, I'll report some findings after this weekend. I still think the basic idea is sound, but the instrumentation needs to be refined to provide valid data.

Gravy