PTO Horsepower Rating?

[M37M35]

So this quarantine has given me time to work on some projects that have been on the back burner. ...And come up with new ones, which leads me to this question...

My deuce currently has the standard front winch powered by the stock transmission PTO. It also has had a knuckle boom added, with the hydraulic pump being driven by a transfer case PTO.

I would like to add a rear drag winch behind the cab between the frame rails for a gin-pole setup, winching equipment on to trailers, unsticking stuck vehicles, etc.

I could tap into the boom hydraulics and add a valve and motor to power the rear winch, but I kind of like the old-school K.I.S.S. simplicity of PTO driving it. To do that, I would have to use the transfer case PTO that is currently driving the hydraulic pump. That would require moving the hydraulic pump and running it off a transmission PTO accessory drive. (Anyone know of a good deal on one?) It would be a bit more work, but I've been wanting to move the pump anyway because it hangs kind of low, and is in the way of carrying a spare tire in the stock location. I'll also have to remove it soon to replace a leaking shaft seal.

Anyway, thinking through all that got me to wondering something... Does anyone know what the horsepower rating is for the transmission PTO accessory drive? Or either of the other two PTO's?
From my research (Which is difficult, because "PTO" is too short of a search term), the accessory drive is used to drive the hydraulic pump on deuces with the dump beds. I found a reference that said it was a 10 GPM pump but didn't mention what pressure, which doesn't let me calculate horsepower required.
I'm asking because my current pump is pretty good size. I haven't found the exact specs for it yet, but I'm guessing 15-20 GPM @ 2,500-3,000 PSI. The boom calls for 2,600 PSI @ 11GPM, so it's at least that. That requires 20 HP.
Worst case of 20 GPM @ 3,000 PSI requires 42 HP.

I would think the transfer case PTO is plenty strong, but any idea about the accessory drive?

Thanks!

 

[cattlerepairman]

According to TM 9-2520-246-34 the Deuce pto puts out 27 hp at 1000rpm.

If I had to install a drag winch and could choose between going hydraulic or PTO, I'd take hydraulic in a heartbeat.

Straightforward flexible plumbing and much safer, accurate control.

Sent from my SM-G950W using Tapatalk

 

[M37M35]

Thanks for the reference! I hadn't found that.

Unfortunately it doesn't specifically list the HP for the accessory output, unless it's the same as the winch output. Except the winch output is 1 1/4" dia. and the accessory output only 7/8", if that makes any difference. Yet the transfer case PTO shaft isn't much bigger at 1 1/2", and it's rated for the full HP of the engine which is what, 135 HP?
Also, I think I remember reading somewhere that the accessory drive turns about the same speed as the engine. I wonder about ratings at say 1,500 or 2,000 RPM?


I agree a hydraulic driven winch is more user friendly and I may very well go that route, but I do want to explore the PTO option.

 

[M37M35]

It looks like @gringeltaube is an expert on these PTO's. I would appreciate your wisdom! Any idea what the useable horsepower would be from the accessory drive PTO?

Thank you!

 

[gringeltaube]

.....is an expert on these PTO's.

Expert? No. Experienced maybe, from having rebuilt quite a few and seen where they normally fail...
The weak- or better say limiting link -(torque wise) seems to be the primary gears in the PTO, not the size of the shafts. So I guess that the given rating of 27hp @ 1000 rpm may well apply to both, front and rear outputs.
Then, regarding wear, what always goes first is the shaft and bearings of the PTO input (driven)gear.

I'm not sure about the pump specs for the hoist of the M-817 dump 5-ton, to compare with your existing (crane)pump. If it really was that much bigger you could always limit pressure and flow. That is, if you really ended up with your pump powered by the rear auxiliary drive.

 

[M37M35]

Expert? No. Experienced maybe...

Well thank you for your experienced insight!

It's good to know what the weak links are and what usually fails. I'll go with the rear output being good for 27HP. I'll track down the specs for my pump and see what the HP requirements would be.

Some additional info for reference...
Before learning about the 27HP rating, I looked up specs for a couple modern PTO's. It might be apples and oranges, but I thought it might at least get me in the ballpark. It's actually pretty close as they are rated for 33HP @ 1,000RPM. Here's the ratings for a Muncie PTO for the GM SM465 and NV4500. It doesn't list it here, but the rating is at 1,000RPM.

Manufacturer: CHEVY/GMC
Model: SM465 (GMC) (Standard 4-Speed for Chevrolet and GMC for 1968-1991)
Bolt Type: SAE 6-BOLT OPENING
Rotation: OPP
PTO %: 98%
Torque: 175 lbs.ft.
HP: 33 HP
PTO Series: TG SERIES
Transmission Gear: G73
Gear Ratio: 18
Shift Type: C - Cable
Assembly Arrangement: 2
Output Type: B - 1 1/4" RD. 5/16" Key
Special Feature: H - High Torque Code TG 12-18
Model Number: TG6SG7318C2BH
List Price: $1011.02



Manufacturer: NEW VENTURE
Model: NV-4500 (6.34 Low Chevy) (Build date prior to 2-17-94)
Bolt Type: SAE 6-BOLT OPENING
Rotation: OPP
PTO %: 101%
Torque: 175 lbs.ft.
HP: 33 HP
PTO Series: TG SERIES
Transmission Gear: N80
Gear Ratio: 18
Shift Type: C - Cable
Assembly Arrangement: 3
Output Type: B - 1 1/4" RD. 5/16" Key
Special Feature: H - High Torque Code TG 12-18
Model Number: TG6SN8018C3BH
List Price:$1093.26

 

[M37M35]

Okay, so I've thought about this a bit more and done more research, and here's what I came up with. If anyone sees any errors here, please point them out.

The TM gives the following HP ratings for the PTO:
2.7 HP @ 100 RPM
13 HP @ 500 RPM
27 HP @ 1,000 RPM

Since HP varies with RPM, the torque should be constant. Research gives this formula for calculating torque:

T = HP x 5252 ÷ RPM

So:

2.7 x 5252 ÷ 100 = 141.8
13 x 5252 ÷ 500 = 136.5
27 x 5252 ÷ 1,000 = 141.8

So that says the deuce PTO is rated for 141.8 foot pounds of torque.

To find the rated HP at 1,500 and 2,000 RPM:

141.8 x 1,500 ÷ 5252 = 40.5
141.8 x 2,000 ÷ 5252 = 54

So it's rated for 40.5 HP at 1,500 RPM and 54 HP at 2,000 RPM, but the number that really matters here is the torque rating.

As this relates to driving a hydraulic pump, the following formula is used for finding the torque required to drive a pump:

T = (P × D ) ÷ (6.28 × 12 × Em)

Where:
T is torque, lb-ft.
D is displacement, cu-in.
P is pressure in psi.
Em is the pump's mechanical efficiency.

Most gear pumps are 80% to 85% efficient, so we'll use 80% to be safe.
My crane needs 2,500 PSI.

(2,500 x 3.42) ÷ (6.28 x 12 x 0.80) = 141.8

So the PTO can power a 3.42 cubic inch displacement pump supplying 2,500 PSI.
If a person needed 3,000 PSI, the pump would have to be smaller. For 2,000 PSI, it could be bigger.

To find Gallons Per Minute of the pump:

RPM x D ÷ 231 = GPM

So if I run a 3.42 cu-in pump at 1,000 RPM supplying 2,500 PSI, that gives me a flow rate of 14.8 gallons per minute.

1,000 x 3.42 ÷ 231 = 14.8
1,250 x 3.42 ÷ 231 = 18.5
1,500 x 3.42 ÷ 231 = 22.2


The speed of the PTO accessory drive turns at 975 RPM with the engine running at 1,000 RPM, which is almost 1:1 so that's easy to figure.
Thanks again to Gringeltaube for the information supplied in this thread!

I got this info by web searches and an old hydraulics handbook.
Some helpful links:
Here.
Here.
Here.


Hopefully this will help other folks calculate a pump or other load powered by the PTO!