Hydraulic pump, motor and such

[Ljohnsaw]

Some of you might remember this old thread of a Case Davis 4wd trencher I picked up a while back:
Case Davis Trencher

Well, the old Kohler engine gave up - connecting rod came loose and inspecting the engine, the cylinder was oversized and oval.  No short block to be found.  So I put an ad out for a horizontal engine in the 16 to 20 hp range (old one was 16).  Bought a 20 hp Onan twin cylinder from a big golf course mower.  It has the shaft out both sides and I'm using one to power the trencher as usual - two hydraulic pumps and a 5-v belt with a clutch for the digging chain.  The two pumps work off a common tank.  One powers the drive (the larger pump) and the other powers the chain lift arm, the steering ram and the two rams on the blade (all small rams).

My intention for this machine was to use it as a base for a 46" snow blower (from a Club Cadet).  The other output is a double groove pulley that I'm thinking of running another hydraulic pump.  This pump would then run a hydraulic motor to power the snow blower head.  I would hang the head in place of the blade.  That would give me the ability to lift and turn it from side to side, if needed.

So, the question is, what type of pump and motor would be suitable to drive the blower?  It currently has a cobbled on 7 hp engine that seems to have enough power but more would be better.  The old 16hp was enough power to run the chain and drive.  So I figure with the extra 4 with this 20hp, I should be good to go.

First question:  I've heard that a hydraulic motor can be used as a pump and some pumps can be used as a motor.  Is there a specific type of pump that is better/more efficient than just using a motor?

Next question:  I already have a variable flow valve that I was thinking of using to set the max flow rate to the blower and then just using a one-way lever valve to turn it on and off.  It sounds like I need the "open center" setup to bypass the oil when not running the blower, right?

Final question:  The trencher currently uses ATF as the working fluid (per owners manual).  Can that be used for this new circuit as well (so I can use the common tank)?  The tank holds about 5 gallons.  I don't think heat build up would be much of an issue as I would be running this in the winter.

But, I will have quick disconnects to remove the blower.  I could then attach a wood splitter in the summer...

[mike_belben]

You should be able to run ATF in any of the variable displacement piston pumps or gear pumps.  A boatload of deere and cubs ran sunstrand 15 hydros with atf still going strong almost FIFTY yrs later.  

I build a lot of junk like youre describing..  My advice, consider putting a gas engine on the blower with a remote throttle control and kill switch.  Itll be cheaper and much simpler than additional hydraulic.  I built a front mount flail for my deere 140 and a $99 harbor freight motor has been plenty of power, excess even.. Itll chew up dense overhead briars at half throttle.  If it fails, hundred bucks, easy changeout, done. 





I have one of those 20 horse opposed onans on my case 448 and its been a huge disappointment, very aggravating to work on.  The whole tractor really.  Despite their huge, loyal following. I think the k341 you have is a much better engine imo.  

[Ljohnsaw]

Well, I already have a gas motor powering the blower.  I was thinking it would be simpler to have one engine to run rather than two.

Very disappointing to hear your dislike of the Onan.  I got it installed today and it just need a little work on the carb - won't run/idle without a lot of choke.  It runs so much smoother than the Kohler and quieter, too.

[mike_belben]

smooth and quiet i will give it, they are.  ive had a pile of ignition trouble, and on the 448, getting at the starter is outrageous.  nose off, oil cooler and fan and a ton of shrouding off. then the entire pto and stub shaft off which isnt easy at all, then the rest of the tin and even air cleaner off.  i mean genuine why did they do this wrench throwing you have got to be kidding me outrageous. the case wrapper is much of the issue but a starter is a pretty chronic wear item and should be right there on the surface IMO.  on a kohler they are. the oem is very proud of onan parts too.  

if you have enough parts and maybe some hoses for a good head start on hydraulic blower it makes sense, but if you have to buy it all id say youll be into it for $400 and thats a few harbor freight engines or one electric start whopper with warranty. the predators are an identical chinese honda clone.  i dont like that the world works that way, but it does.  theyre a really good cheap engine that i cant afford to avoid.

[Ljohnsaw]

Mike,
Since this came out of Toro Groundsmaster and I didn't get a wiring harness, I'm wondering about the oil sending unit.  Is that supposed to be wired to an idiot light or in line with the ignition to kill the engine on low oil pressure.

[mike_belben]

On the onan?  

Im sorry but i dont know, ive never noticed one on mine.. Its probably buried under tin if there is one.  Or gone since mine is kinda hacked up by prior owners.  


I will guess that the oil pressure switch illuminutes a dummy light by closing below a set PSI and completing a bulb circuit to ground if its single wire. 

If the oil pressure switch was grounding the ignition coil you probably wouldnt be able to start the engine without some sort of delay timer on it that ive never encountered.. I dont think a slow cranking engine will generate any oil pressure but i have definitely had mine start on many occasions just as the cranking speed was approaching none.. Then pop pop poppopopop as it catches.  I cut up a toro reelmaster years back and it had a kohler.