A case study in centrifugal pump protection using flow controllers

Last issue we looked at the benefits of flow controllers as a tamper-resistant method of protecting centrifugal pumps from possible damage and/or failure caused by running them off their curve. This case study, using a Maric flow controller, demonstrates this in practice.

Case study: Franklin FPS1A-13TS pump

Using a Maric flow control valve for pump protection in a high standing (high draw-down) water table condition.

The Franklin FPS1A-13TS pump suits the application at the 85m draw down level, however, it will run off the right hand side of curve with only 20m head against pump at start up resulting in pump and motor damage.

Installation details: 
Franklin FPS1A-13TS

Manufacturers performance curve below indicates flow should not exceed 1.4m3/hr (23L/min).

Graph1

Manufacturers performance curve

Pump protection requirement

To prevent pump and motor damage due to upthrust condition we must limit flow, or add sufficient head, during start-up.

Three options are available:

1. Gate valve: They are cheap but can be noisy and can also result in a high headloss at the duty point, reducing pump output. As these valves can be adjusted by anyone, they are not tamperproof, and are often opened all the way in the endeavour to get maximum flow and can fail due to the gate vibrating loose.

2. Pressure sustaining valve: These are expensive, adjustable and can result in a potentially high headloss at duty point, reducing pump output. Again, as they are adjustable, they are not tamperproof, and are often opened all the way in the endeavour to get maximum flow.

3. Flow controller: These are the best solution for a high standing water table condition, with lower duty point conditions.

Graph2

Pressure differential across valve

 

Flow controllers are tamperproof, inexpensive and result in a low headloss at the duty point as can be seen in the graph above.

Question:

What will the headloss be across the Maric valve and its effect on pump performance at the 85m duty point?

Answer:

Very little. Around 4 metres.

Why? 

At 85 metres drawdown (and resulting head against pump), flow rate will be 0.85m3/hr (14 lpm) only. This is 60{87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf} of the rated (23 lpm) flow of the flow controller, and at 60{87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf} of flow through the Maric valve, the pressure differential (or headloss) is around 4 metres only, having little impact on pump output.

Flow control valve performance:

Flow control valve performance curve above indicated 60{87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf} of rated flow = 4 metres headloss only (see x).

Conclusion:

As in the above application, and many similar cases, the Maric flow control valve is an excellent choice for pump protection, due to its lower headloss, cost effectiveness, long maintenance free life and being virtually 
tamperproof.

See our previous issue for Part 1 where we provide an overview of pump protection.

 

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