need help choosing hydraulic pump

memphismark · Jan 11, 2016

Hey guys'. I need help choosing a hydraulic pump for an auger drive that I use to spin a 2 yard concrete mixer I fabricated at the shop. I have a 22 HP motor that I'll use, and the auger drive is an Omni unit rated @ 8-12 GPM. I've been purchasing everything from Surplus Center so far. Using a Prince 20 GPM spool with a Prince cushion valve (rated @ 1500-3000 PSI) between spool and auger 'cause I had some problems with popped hoses due to deadheading. Surplus has a calculator saying approx. 1.6 cubic inch pump would work. Any suggestions. I'm a total novice and experience from people on the forum would give me some much needed 'piece of mind'. Used the auxiliary hydros on my Bobcat 753 up to this point, but I need to free up the Bobcat and not have it tethered to the mixer. Need lots of torque. thanks much. memphismark

Texasmark · Jan 11, 2016

Northern Tool has a lot of hydraulic parts, some of which are reasonably priced (opinion some folks may think they all are).

I bought a 16 gpm pump from them several years ago that hooked to a gas engine....8 hp required for that minimum. Put out around 2500 psi. Pump needs a mounting bracket and Lovejoy connections as it can't stand any lateral (to the side) pressure like you have if you opt to drive it with a V belt or drive gear......no heavy duty shaft bearings to support a lateral load. The Lovejoy connectors take all pressures off the pump drive shaft except the reciprocal pressure of the shaft turning. Open center valves are for sale too with different operational features. The one for log splitters is auto reset and a real buy; works great as does the pump.

oldnslo · Jan 12, 2016

memphismark,
What are the specification for the Omni unit. You state 8 - 12 GPM but what is the pressure? What RPM is desired?

What RPM is your 22 HP motor?

In theory you can pump around 13 GPM @ 2500 PSI with a 22 HP input.

atached is a sheet with hydraulic formulas for calculating pump displacements, motor torque, speed, etc.

Texasmark · Jan 12, 2016

The one I mentioned mounts directly to a horizontal or vertical shaft BS type engine. So, for what I stated, 3600 rpm for a governed rpm design spec......course now that I have machines with tachs, seldom do they run 3600. Usually more like 3300 course that could be do to the adons that aren't on the "brake HP" testing when the engine is spec'd...like air cleaner, muffler, v belt running loose in a chev., ambient temp and altitude.

memphismark · Jan 12, 2016

The problem is that the gear motor is on the inside of a large black, square steel housing and there are no visible numbers, HP or otherwise, that I can see. Omni only say's 8-12 GPM. Also, since I bought the auger on eBay, Omni tech guys won't even speak to me. The housing protects from auger debris and makes a way for it to dangle' from a skid steer. It also helped me mount the thing for my use. The gear motor inside the housing turns approx. 40-50 RPM, which happens to be a good speed for mixing concrete. When I start mixing, load is the highest and my line pressure gauge say's we are in the 2400 PSI range, sometimes spiking to 3000 and causing the relief to squeal like a pig! While after mixing a bit and the water puts everything into solution, pressure drops to 700 PSI or so, and the Bobcat can practically do this at idle. So it goes from needing a lot of pressure to not a lot of pressure. I have learned (about hydrualics) that the pump does not create pressure, but the load does. It's taken awhile for me to get to where I understand that the pump is about flow numbers, not pressure, and that's what has me confused because I don't understand what the effect of cubic inches does in this equation. Since there are small HP motors, say 5 HP that can make a particular pump get to 3000 PSI, why can't that 3000 PSI turn a big motor like mine? 3000 PSI is 3000 PSI, right? Apparently not. That's where, I think the whole 'cubic inches' thing comes into play. Boy would I love some 'schooling' from you guys on this. Basic explanations would be so helpful. Any thoughts anyone??? Thanks so much for responding guys. memphismark

oldnslo · Jan 12, 2016

Since you know the flow required you can use this to figure pump size based on the drive engine RPM.

formula is: GPM = (CIR x RPM) / 231 or transposed CIR = (GPM x 231) / RPM

GPM = 10
RPM = 3000
CIR (Cubic Inch/rev) = .77 or 12.6 cc/rev

If your motor RPM is 3300 with .77 CIR motor the flow is 11 GPM.

For some safety factor I would over size the pump around 5-10% to help insure that you receive the required flow to maintain mixing speed.

J_J · Jan 12, 2016

What you are looking for is torque, and rpm.

Rpm should be low to med.

The larger cu in, the larger the torque.

If your pump can supply 10 GPM and has a capability 3000 ps, you can drive a 10 cu in motor and have 231 rpm, and 4775 inch lbs. ft lbs = 397

If your pump has 10 GPM and motor is 20 cu in, then you have 116 rpm, and a torque of 9549 in lbs . ft lbs = 795

memphismark · Jan 12, 2016

Surplus Center website has, in it's tech section, a computer/calculator where you can plug in numbers and it spits out computations accordingly. My Omni auger claims 1400 foot pounds of torque, not inch pounds, foot pounds. Omni claims 8-12 GPM for this motor. Are we looking at a 50-60 cubic inch motor? I have heretofore been using my Bobcat skid steer to drive the auger but that's out.
Here's what I need to know. I have a 22 HP gas motor, it's all I can afford for this concrete mixer, and I need the strongest pump that this 22 HP motor can spin, to get the max torque out of this Omni auger drive. Also, hose sizes. What would you suggest. If I plug info into the Surplus Center computer, a 22HP motor @ 2200 RPM will work with this pump part number: 9-1900-B-R. My fear is that this pump is just too small for the aforementioned auger motor, especially if it's 50 cubic inches.. What would you think of that pump choice. Thanks. memphismark ps....I wish I knew how to send you a direct link to the pump, but I'm just not that computer savvy. Maybe you know how.

oldnslo · Jan 12, 2016

Memphismark,
First: I suspect there is some form of gear reduction unit in the Omni. A 50 -60 cubic inch motor is big and heavy.

Second, Pressure gives you torque while flow gives you speed. There are pumps capable of 5,000 PSI but what is your Omni unit rated for?

memphismark · Jan 12, 2016

I have been using my Bobcat 753 auxiliary hydraulics to spin the auger for a concrete mixer I built but I can't do that anymore. The Omni auger has no info other than what their website say's which is 8-12 GPM and 1400 ft. lbs. of torque. Not inch pounds, foot pounds, which is massive. Unfortunately I have no idea about the pressure or cubic inch rating of the auger motor. And yes, I'm sure there is a gear reduction of some sort. The unit weighs around 140 lbs. and that can't just be the motor, but it's inside a protection housing I just cant' see anything. The 22HP motor that I plan to spin a pump with is all I want to invest so I just need the maximum pump this 22HP motor can spin get everything out of the auger drive I can. Most of the torque is used when the mixer is just starting and the sand, water and cement are separated. That's the hard part, after the water get's everything nice and loose, much less torque is needed. The Bobcat could easily handle that part idle, but probably 2300 RPM or more in the beginning to get it moving.. Any thoughts about a pump???