Viewpoint: making the case for valveless flow control

For many engineers it is logical to use a centrifugal pump and a control valve for flow control applications such as wastewater treatment, chemical metering and ingredient addition.

However, progressive cavity (PC) pumps are particularly well-suited for these applications due to their valveless design, controllable flow and low pulsation.

Typically, PC pumps can replace centrifugal and control valve combinations in any application in which flow control is vital.

For instance, transferring slurry to a blending tank would typically prompt the need for a centrifugal pump and a control valve to control flow, but a PC pump should be considered.

The term for the use PC pumps in this way has been coined ‘valveless flow control’.

Abundant advantages

PC pump advantages include reliability, easy calibration, low pulsation, reduced maintenance, capital, and operating and energy costs.

Various ranges of PC pumps can precisely meter and gently convey fluids of any viscosity, in a wide range of temperatures, with or without solids.

In a PC pump, a single helix rotor turns insides a double helix stator to create cavities that progress from the suction to discharge.

The compression fit between the rotor and the stator creates seal lines that keep the cavities separate as they move through the pump with each rotation.

Valveless flow control with a PC pump is an option for your flow control application that offers significant benefits and advantages over other pump types

The compression enables the pump to act like a valve. The result is flow with very little pulsation and low shear rates. Slip is also less of an issue and when the pump stops, nothing will flow through it. The compression between the rotor and stator even enables customers to mount the pumps vertically.

It is feasible that valves could be eliminated altogether.

PC pumps can also solve a multitude of flow control issues compared to other pumps that require control valves. When considering process control, a progressive cavity pump, flow meter, and Variable Frequency Drive is much simpler than a centrifugal pump and valve combination.

A PC pump self-primes and acts as a pump and control valve in one, providing much better flow control.

Furthermore, PC pumps are not affected by changing pressures. Hysteresis and modulation can be virtually eliminated, and there is no worrying about internal or external air leaks or obstructions in the suction or discharge pipework.

Flow success

Recent innovations in PC pump technology such as Smart Conveying Technology (SCT) and the success of several flow control installations at chemical process plants has resulted in proof that using a PC pump improves performance and cuts costs.

The SCT design allows the stator to be re-adjusted due to the integrated re-tensioning device, giving longer stator and rotor life. By separating the stator into two halves, PC pumps with SCT will reduce service times substantially and no longer have to be removed from the installation for maintenance.

Cutting costs

When comparing the costs of both potential flow control solutions, be sure to compare the cost of a PC pump to the combined cost of a centrifugal pump and control valve. The control valve‘s power medium is often compressed air, one of the most expensive sources of energy in a plant.

Valveless flow control with a PC pump is an option for your flow control application that offers significant benefits and advantages over other pump types.

• Peter McGarian is director at pumps manufacturer Seepex