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Q: calculate rpm for two hydraulicly driven motors with given information ( Answered 5 out of 5 stars,   0 Comments )
Subject: calculate rpm for two hydraulicly driven motors with given information
Category: Science > Physics
Asked by: ptonyc-ga
List Price: $10.00
Posted: 23 Mar 2005 11:41 PST
Expires: 22 Apr 2005 12:41 PDT
Question ID: 499272
Determine the maximum speed in rpm of two hydraulicly powered motors A , B
using the following information:
Electric motor that drives hydraulic pump rpm = 1750
Electric motor drive pulley = 3 3/4" diameter
Hydraulic pump displacement = 6.0 GPM @ 1200 rpm
Hydraulic pump pulley = 5 1/4" diameter
Motor A displacement = 10 cu inches
Motor B displacement = 3 cu inches
I need to find:
Motor A max rpm___________
Motor B max rpm___________
Subject: Re: calculate rpm for two hydraulicly driven motors with given information
Answered By: redhoss-ga on 23 Mar 2005 16:35 PST
Rated:5 out of 5 stars
Hello ptonyc, here is the solution you require:

First we must determine the speed at which the pumps are driven.

RPM of pump = 1750 x (3.75/5.25) = 1250 

Since the 6.0 GPM is given at 1200 RPM we must calculate the delivery
rate at 1250 RPM.

GPM of pump = (1250/1200) x 6.0 = 6.25 GPM

Converting GPM to cubic inches per minute.

6.25 gal/minute x 231 cubic inches/gal = 1,444 cubic inches per minute

Now we can calculate the RPM of the two motors.

Motor A: 1,444 / 10 cubic inches per revolution = 144 RPM

Motor B: 1,444 /  3 cubic inches per revolution = 481 RPM

Please let me know if you don't understand anything I have done. Ask
for a clarification and I will try and explain further.

ptonyc-ga rated this answer:5 out of 5 stars and gave an additional tip of: $10.00
We are setting up the said pumps and motors and will test final rpm
with a hand tachometer on Saturday, March 26, I will advise what
actual hand tach tests out at.  I don't know if your calculations will
come out correct but I do believe it will be close.  Thank you so

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