need help choosing hydraulic pump

[LD1]

What would be the effects of trying a bigger pump with same 22HP motor? Say 16 or 18 GPM pump? memphismark

You will stall the motor or be forced to operate at a lower pressure

The formula is HP=(PSI x GPM)/(1714 x % efficiency)

To get more pressure, you are going to have to use a smaller GPM pump. To get more GPM, you are gonna have to drop the PSI. It really is that simple.

How all this relates to the mixer......more flow is NOT going to make it more powerful. Its only going to make it rotate faster. More pressure is going to give it more torque.

Dont get too greedy on GPM's. Having the ability to rotate fast dont to any good if it wont spin at all. Follow the MFG specs of 8-12GPM. That will allow you to get the full 3000psi out of your 22hp motor.

Depending on the efficency of the pump, (assuming 85%), 10.7gpm is about max at 3000psi. And for a 3200rpm motor as you have, that would be a 0.77 cu in pump MAX.

Surplus center sells a 0.73 cu in pump. That would be what I would get. Puts you right on spec for flow on the mixer, and will get you the full 3000psi you need when starting a load

 

[J_J]

A cement mixer should not turn no more than 30 to 50 rpm.

Torque is good. You have plenty of HP to turn the mixer.

If I remember right another TBN member used a 3.0 cu in motor and then geared it down to a slower rpm.

http://www.tractorbynet.com/forums/hydraulics/154151-pto-cement-mixer.html#post1772452

Pump volume can be controlled by the speed of the engine.

 

[ishiboo]

I think we're overthinking this.

We already know it runs acceptably on a Bobcat 753. If we know the year and model, we can find out what the GPM/PSI is. For example, a regular old 753G is 14 GPM at probably 3000psi. That's going to be more than 24HP. I would personally look for something around 8-9 GPM assuming that 22HP is a 22HP gasoline engine. That will put you in the ~1.2 cu/in range. You'll want to run it just about as fast as you can for rated output. You can dial down the engine RPMs as necessary. The pump will need to be specced to operate in the RPM range you are looking for - a 3000RPM rated pump (probably 3600RPM max) would be great, not sure how much luck you're going to have finding it though.

 

[memphismark]

Sorry guys, I'm on west coast time and you are 3 hours ahead of me. I'll catch up. You are correct, it is a 14 GPM Bobcat 753, a 2003 year, 42 HP I think. The 22 HP motor I'll drive the pump with is gasoline. I would love to run the 22 HP motor at 2200 or less if possible, just so I don't have to listen to it. It's not the quietest little thing. Probably not practical though. Max, efficient output of pump is what I'll need to get the most out of the motor, and it sounds like everyone is agreeing about 1.2 cu.in. or so. Yes, no, maybe? memphismark

 

[memphismark]

Sorry guys, I'm on west coast time and you are 3 hours ahead of me. I'll catch up. You are correct, it is a 14 GPM Bobcat 753, a 2003 year, 42 HP I think. The 22 HP motor I'll drive the pump with is gasoline. I would love to run the 22 HP motor at 2200 or less if possible, just so I don't have to listen to it. It's not the quietest little thing. Probably not practical though. Max, efficient output of pump is what I'll need to get the most out of the motor, and it sounds like everyone is agreeing about 1.2 cu.in. or so. Yes, no, maybe? memphismark

 

[oldnslo]

1.2 cu.in. @ 2200 RPM provides 11.4 GPM What HP does your motor develop at 2200 RPM? I think you would be very disaapointed with this size pump since you wouldn't be able to build enough pressure to turn the mixer at start-up.

From your earlier posts you need 2500 - 3000 PSI to get the mixer going for the first few revolutions so you need to size the pump to allow you to get that pressure range.

Based on the full 3200 RPM you can drive a .75 cu in pump at 3000 PSI.

 

[LD1]

I think we're overthinking this.

We already know it runs acceptably on a Bobcat 753. If we know the year and model, we can find out what the GPM/PSI is. For example, a regular old 753G is 14 GPM at probably 3000psi. That's going to be more than 24HP. I would personally look for something around 8-9 GPM assuming that 22HP is a 22HP gasoline engine. That will put you in the ~1.2 cu/in range. You'll want to run it just about as fast as you can for rated output. You can dial down the engine RPMs as necessary. The pump will need to be specced to operate in the RPM range you are looking for - a 3000RPM rated pump (probably 3600RPM max) would be great, not sure how much luck you're going to have finding it though.

8-9gpm is NOT 1.2 cu in range. 1.2cu in at his motors rated RPM is going to be closer to 16GPM. Which his 22HP will only be able to operate up to 2000psi and that wont start his mixer load based on what he says.

Max, efficient output of pump is what I'll need to get the most out of the motor, and it sounds like everyone is agreeing about 1.2 cu.in. or so. Yes, no, maybe? memphismark

Better re-read. I dont see anyone other than the last poster "agreeing" on 1.2GPM. The formulas are stated in this thread several times. Do the numbers.

And I dont think you are gonna want to run that at 2200RPM. You will likely be cut down into the 16HP or so range and would have to re-figure accordingly. But thats just a guess. The motor is going to be most efficient at rated 3200rpm

1.2 cu.in. @ 2200 RPM provides 11.4 GPM What HP does your motor develop at 2200 RPM? I think you would be very disaapointed with this size pump since you wouldn't be able to build enough pressure to turn the mixer at start-up.

From your earlier posts you need 2500 - 3000 PSI to get the mixer going for the first few revolutions so you need to size the pump to allow you to get that pressure range.

Based on the full 3200 RPM you can drive a .75 cu in pump at 3000 PSI.

Agree. Your numbers seem to match about what mine do. Something around .75-.77 GPM is the max he can spin.

 

[memphismark]

After much consideration I agree that the smaller .75 cubic inch range pump would be best. You are right again, that trying to hold down my 22HP motor to 2200 RPM will likely net 15 or so HP at best, and keep me well below the pressure ranges you guys suggest I will need. I am grateful for all who chipped in to help me on this one. This is a great web site. Gentlemen, I pronounce this case closed. Amen. Thanks guys. memphismark