Valveless Flow Control

Experience a paradigm shift

Did you see a duck or a rabbit? You may have seen a duck or you may have seen a rabbit, but at first glance, you probably decided what the image was of and that is how you will continue to see the image going into the future, unless your point of view is prompted to change. A paradigm shift is a change from one way of thinking to another. It does not just happen, but rather is driven by an agent of change. Chemical Bob is an agent of change who wants to help you experience a paradigm shift from centrifugal pump and control valve combinations to valveless flow control with a progressive cavity pump.

Stop thinking control valve

There are current paradigms, or methods of thinking, that limit progressive cavity pumps in flow control applications. For many the logic is to utilize a centrifugal pump and control valve for flow control applications. Common issues with centrifugal pump and control valve combinations include cavitation, leaks, obstructions, erosion, hysteresis and modulation. Centrifugal pumps can lose prime between batches or from alternating pumps. And if a control valve fails, the only choice is to repair or replace it. Control valves could be eliminated altogether.

Start thinking valveless flow control

The term for the innovative use of progressive cavity pumps in flow control applications has been coined “valveless flow control”. A progressive cavity pump is much simpler than a centrifugal pump and control valve combination. 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. The compression enables the pump to act like a control valve and pump in one. Valveless flow control technology enables the elimination of control valves and an increase in flow control performance.

The centrifugal pump’s best efficiency point should be considered. Calculate HP for 20, 40, and 60 GPM using the 8.5” impeller vs. a seepex BN 17-6L PCP. Although starting HP on the seepex is higher (for a brief second), BHP is lower. As a standard rule of thumb, a PCP will provide better efficiency when PSI is greater than the GPM. This makes PCPs ideal for flow control applications requiring low flows and high pressures. A seepex BN 17-6L PCP has much better efficiencies than a centrifugal pump.

The advantage of valveless flow control

Progressive cavity pumps are well suited for any application where flow control is necessary due to their valveless design, controllable flow and low pulsation. Various ranges of progressive cavity pumps can precisely meter and gently convey fluids of any viscosity, in a wide range of temperatures (especially with even wall stators), with or without solids. A progressive cavity pump self-primes and provides much better flow control.

A historical graph produced by a control room illustrates the difference a PCP makes when it comes to flow control. The graph shows the control valve modulating as it tries to respond to the flow setpoint, which leads to a wavy line. The centrifugal and control valve combination was taken offline just before 11 a.m. and replaced with a PCP. The data showed the PCP’s flow rate “flatline” and the difference is obvious. The PCP reliably displaced an exact volume per revolution and was not as affected by downstream pressure changes, leading to highly reliable flow control.

When comparing the costs of both potential flow control solutions, be sure to compare the cost of a PCP to the combined cost of a centrifugal pump and control valve. The cost of a complex control valve and actuator combined with a centrifugal pump often exceeds the cost of a PCP by 1.25 to 1.5 times.

Capital, energy and maintenance costs will be lower, especially with Smart Conveying Technology. SCT reduces service time by up to 80 percent. This technology splits the stator axially into two halves and compression fits the segments together using four retaining segments.The segments increase the life of both stator and rotor with just a simple adjustment while also allowing easy access to parts for inspection without the need to dismantle pipelines. A progressive cavity pump with Smart Conveying Technology (SCT) is extremely easy to maintain.

Read Chemical Bob’s story

Chemical Bob wants you to see reliable valveless flow control and reduced capital, maintenance, operating, and energy costs. Experience the paradigm shift from centrifugal and control valve combinations to valveless flow control with a progressive cavity pump. Read the story.