Coupling a Diesel Engine to a Pump

David,

I would not expect the radial load on the crankshaft of your diesel engine to be much different from the manner in which a crankshaft is loaded when the engine is coupled to an otherwise conventional transmission. The lower end of that engine has been designed to withstand torque, or significant rotational moments from its outset.

Note, however, that things get pretty busy at 3000 and 2500 RPM respectively. Many of the issues that plague conventional auxilliary engine installations will apply here (e.g., driveshaft alignment, vibration dampening, proper isolation of the installation from mounting fixtures, failure containment systems, load application sequence, throttle control, etc..).

If there are any available standards related to your installation or application, you'd be well served to become familiar with them (e.g., SAE, ASME, API, etc..).

You ought to be just fine if you're careful.

Using a approved stub shaft bolted onto the flywheel is possible and under the right conditions even without external bearings. The manufacturer of the diesel however could set conditions which must be satisfied.

Another option is to look at machining down the impeller to deliver at 3000 rpm (or slightly below). Check with the supplier of the pump.

Another option may also be to select another pump which will be able to match the duty point at 3000 rpm (or whatever speed is required for the diesel).

One of the last 2 options using a direct coupling would beat using a v-drive. (Have a look at the drive losses)

David,

I would suggest to you that you consult the manufacturer or agent to get a bolt on Clutch PTO, then belt drive the pump using proper sheave sizes and number and size of Vee belts to obtain desired operating speeds. The clutched PTO will have bearings in it to withstand the radial load, also will allow starting and testing/service of the engine without turning the pump. I do suggest that you size the sheaves to operate the engine at lower speed if possible, (Will engine develop enough power at slower speed to satisfactorily drive pump?), as lowering the engine speed will reduce fuel consumption, and lengthen the engine life, remember friction is a quadratic function of speed, and engine life approximately also.

Regards CEKM

Avoid the belt drive if at all possible, they add to the maintenance bill.

Skimming the impeller would be the most elegant solution if it is possible in your case. The pump manufacturer is best qualified to give you the new curve at 3000 rpm and the impeller diameter required to meet your needs. If you can not get information from him then calculate it for yourself. First correct the curve for rpm. H1 = (n1/n)^2 *H, then calculate new diameter for required H. H1 = (d1/d)^2 * H.

As you are only varying the head by about 9.5% with your increase in speed and reducing the impeller by about the same percentage it should be no problem to reduce the impeller diameter.

You may also want to consider fitting an orifice in the discharge of the pump to steepen the curve to achieve your operating point at the new operating speed.

If the engine can be direct mounted to the engine, do it. If you can do it with a disconnect device, even better. Run the engine at the most efficient speed. If there is too much pressure, dump it back into the suction. You can install a pilot operated relief valve, or a simple spring loaded relief valve, to adjust the max pressure.

As an added side benefit, the system will automatically adjust to maintain the desired pressure as pressure losses occur, from wear, or as water is used.

You did not state the flow of your system, but based on a 3000 RPM diesel speed, I would think it is a small engine, and about 3000 GPM pump.

Better questions will yield better answers.

What is rated power capacity of diesel? For what you will need hydraulic pump?

And also, what is needed power capacity of pump? Does this deisel dedicated to move the pump only?

Born and raised in the bush. Diesel engine to pumps all shapes and sizes. Smaller pulley to bigger pulley always done. Bolt pump to tensioner rack, if you havent got time to very very occasionsy put a spanner to the tensioner bolt and give it turn, give up, go home, put the whole thing in the paper and use the proceeds to buy beer.

Cheers

Peter

"Can I radially load the diesel engine crankshaft bearing by attaching a pulley to the fly wheel with a shaft and bearing assembly?"

No you can not load the crankshaft bearing period.

To accomplish this correctly you will need a PTO. Twin-Disc is the more common for this application.

When you use the PTO you can also add the option of easily engaging/dis-engaging the driven equipment. The most important is that the PTO is designed to support such loads with two taper roller bearings supporting it's shaft, the side load is then transfered to the engines bell housing.

Your crankshaft does not support any side load to speak of when the engine is coupled to a transmission as some have suggested. It is only used to center and support the input shaft in this fashion.

Attach four groove pulley to fly wheel. Finger tightening of tensioner bolt will suffice.

Cant understand where radical load is coming from, is there something your not telling us?

Cheers

Peter

Darling Duro Pumps use to have a hydraulic torque converter that would keep the pump running at a specific speed and presure. It almost worked like a VFD on a motor but opposite, the motor could run at any speed and the pump would only be allowed to run at the torque converter setting anywhere from 1 rpm to what ever the rpm is on the motor. This torque conveter acted as a coupling between the motor and the pump. I imagine you could bolt it directly to you flywheel of your motor, just like an automobile. I also believe Armstrong Pumps bought out Darling Duro a number of years ago.

Interesting

I agree with Tim - South of the Rio Grande -

Side (radial) load the crankshaft and you can kiss that engine adios.

Certainly not something you would advise someone to do in good faith anyway. Unless this is simply a low budget quick fix and the engine has little or no value

In many instances diesel engines are designed to support the front half of a generator rotor that is designed with one bearing on its rear housing. AB-20 for instance.

You will also find that provisions have been made specifically for this. For instance, EMD engines have a rear main bearing that is 2-3 times larger than its other main bearings.

I also believe this is acceptable due to the fact that it is a balanced rotating mass rather than a radial load applied by a belt or chain drive.

The above is also true for Detroit Diesels (EMD's baby sized counter part)

You don't really give us a lot of information about your application. However, if you know how much flow you need/want, fashion a coupling that will couple the motor shaft to the pump shaft. There may be some commercially available couplings that will accomplish this such as Lovejoy and Falk among others. If the motor has no shaft sticking out the front, then make a stub shaft as someone earlier said and couple this to the motor shaft. Align it and turn on the motor.

If the flow you need is accomplished at a speed lower than the 3000 RPM rating of the motor, slow it down. If not, speed it up. The pump doesn't care what speed it runs at (within reason, of course) and the horsepower expended will not matter since this is not an electric motor. If the motor can't develop enough horsepower to give you the amount of flow you need, it simply will not achieve that speed. As you slow the motor down (and thus the pump) the flow will decrease until the required flow is met. Monitor the flow during that exercise. When your point is reached, lock the pump in at that speed.

This is not a difficult task. The result may not be the prettiest contraption ever built, but you can make it work. Again, a lot depends on your needs. Play with it a bit. Use your imagination. You can put a governor on it to maintain the speed you require and you can adjust up and down as needed. Lots of options. Report back. Let us know.

David,

How big is the engine? Rate HP at 3000 RPM? Rated HP at 2500 RPM?

How big is the pump? Inlet and Discharge pipe size? Flow and Pressure at 2500 RPM?

What flow and pressure will be required at the discharge of the pipe?

The answers so far are:

Radial loads don't matter, go for it.

Radial load are a problem, don't do it.

Both answers might be correct, it depends on whose engine and the size of the loads involved. Providing horspower, flow, and pressure information will provide a better answer. and perhaps the power requirement is low enough that you could throttle the engine to 2500 RPM and live with the de-rated engine output/efficiency.

No need to worry of the rpm max rating of the diesel engine. Unless you require that amount of hp at max rpm. Diesel engines are load type of engines, the more that is required, the more fuel that will be injected to maintain the governed rpm. Have a look at your output/input curve of both engine and pump. 500 rpm difference is not that much, maybe a compromise of 250 rpm might be in order. Crank shafts do not like radial loads unless they are designed for them. The front of an engine has a pulley on it, to run accessories. The radial load is vertical to the main bearings and and counter weights. A 90 degree load will cause a deflection of the crank shaft and quickly create a catastrophic failure of the engine.

I don't think you have to worry running the engine at 3000 rpm. The diesel engines I have driving my firewater pumps have speed regulators that you can tune down to 2500 rpm.

I think basically you have to find a compromise and maybe operate your pump say at 2700 - 2800 rpm.