How big gas motor to replace 5.5 electric

[mnellis]

I'm looking at a surge dairy pump with a 5.5 hp electric motor. I've been told that I would need a 10 hp gas motor to run it. Can't I get away with a 5.5 hp gas with the proper size pulleys?

Mike

[mountainvan]

It all comes down to torque. A smaller gas engine just does'nt have enough power to spin the larger pump. Either get a smaller pump or the bigger engine.

[Parker]

What model pump are you trying to run?

[mnellis]

Not sure. He claims it pulls 45 to 50 cfm, rpm @ 1100 if that tells you anything.

[Homestead Maple]

To replace an electric motor with a gas engine the factor is 1.5 or 8.25hp or larger.

[Bucket Head]

You should be able to use a 5.5 gas engine with the proper gearing. Five horsepower is five horsepower, regardless of the source.

You need the correct gearing reduction (pulley's or sprocket's) because the gas engine develop's it's 5 hp at a higher RPM than the electric motor. The vacuum pump need's to turn at a much lower RPM, or at least the pump's I've seen do.

A fellow sugarmaker near me is currently setting up their pump with a Honda 5.5 motor. The vacuum pump turn's at 420 RPM. It had an electric motor rated at 1725 RPM. The gas engine has a governed top speed of 3600 RPM, and will probably operate the pump around 2600 RPM.

The engine speed will be reduced with either a 6:1 gear reduction unit, or a jack shaft with the proper sized pulley's on it. We still have to do the math on it.

Steve

[Parker]

Surge had a couple of pumps with 2 heads and the elec. moter in the middel between the heads,both heads were plumbed into the balance tank they sat on,,,that could be problematic,,if that is the case I would suggest useing the 2 heads individually,,I ran one of those heads for a season with a 5.5 honda,,,,,,,,,,one thing with surge vane pumps,,you HAVE to make sure the oilers are working properly {clean} or you will have a pump failure (and mabey a fire like I did)............

[Grade "A"]

As Mountainvan said the differense between the two motors is torque. Torque is what keeps your power when your motor is under a load. This means you will have to rev up the gas engine alot to do the same job as an electric motor, so you will be burning more gas with a 5.5 hp engine than if you got a bigger gas engine because of the rpm's you need to do the job. But if you aready have a 5.5 hp engine I would try it and see what it did. I would hate to see you buy one and find out it was to small. good luck.