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Monday, March 27, 2017
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Variable Speed Drive for Pump Control
Variable speed pump and control

Hi all,

I am going to design closed loop system. my process variable is the flow rate, and i would like to control it using variable speed drive. the pump we use is 3 phase, and it has manual variable speed indicator so i can change the speed manually. it's from Mono Ltd.

please i need your help. still i need a variable speed driver for this pump to adjust my output according to the flow rate comes in? or i don't need to? if i do need variable speed driver, please could you help with which one i can use (specification).

please let me know if you need more information

thank you

1 out of 1 members thought this post was helpful...

A basic requirement for using this pump in a closed control loop is that you will need to be able to adjust its speed by the controller. You say that you now adjust this speed manually. You are missing an important piece of hardware: the actuator that can translate the controller output signal to the pump speed adjustment. I was not able to find such a device in my quick search of the Mono Pump website, but perhaps a Mono Pump sales person can help you.

In any event, the relationship between rotational speed of this pump and flow rate is linear, so you should have no problems in controlling flow, if you are successful in finding an actuator.

Thanks dick caro,

i think no need to actuator as my output controller (PLC) will send the signal directly to the pump wire to change the frequency so that will change the flow (control it) based on the signal comes from the controller. so its like bypass the the manual adjustment. that's what i think and please correct me.

so i still looking for the proper specification for my pump VFD


1 out of 1 members thought this post was helpful...

I have used those pumps to control flocculant in a mining application.
You don't need the manual speed adjustment but you can just leave it set to one spot like a coarse flow adjustment.

I have also seen them with a Raise/Lower speed adjustment (small split phase motor) on the gearbox.

is it possible to use VFD for this type of pump that has manual variable speed (hand wheel)?


I think you answered your own question - YES. All you need is to replace the pump 3-phase motor starter with a VFD sized for that pump motor. Leave the hand-wheel manual adjustment in the maximum flow position, and connect the PLC output (usually 4-20mA) to the VFD configured such that the 4-20mA signal will become the motor speed setpoint. Then 20mA output will be the maximum speed of the pump motor, and 4mA should be zero flow.

>is it possible to use VFD for this type of pump that has
>manual variable speed (hand wheel)?