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Cycle Stop Valves Can Save as Much Energy as a Variable Speed Pump Head produced by a pump drops off by the square of the speed. Pumps that must lift a certain distance or produce a specific pressure (or TDH) have a minimum speed that will accomplish this task. The speed of a correctly sized pump can only be reduced a small amount if a static head or constant pressure is required. Horse power reductions by the cube of the speed can be insignificant compared to a full speed pump simply pushed to the left of it’s curve. Before you can use the Affinity Law the following steps must be taken to determine the minimum speed possible from your pump. The affinity law can then be used to determine the minimum horse power possible from your pump when using a VFD. Total Dynamic Head or (TDH) sets the minimum speed allowed. Divide the (TDH) by the pumps Shut Off Head (SOH). The answer will be a percentage of head loss possible or Possible Head Reduction (PHR). Minimum Possible Speed or (MPS) squared equals the Possible Head Reduction (PHR). (MPS) cubed equals the minimum percentage of Horse Power or Minimum Possible Horse Power (MPHP). For example:
To maintain a Constant Pressure this pump can only be slowed by 9%. This only reduces the Horse Power from 10 to 7.5. Choking back a full speed 100 GPM pump to 5 GPM the efficiency drops to 5%. Using these figures along with a TDH of 277' the standard BHP rule follows. 
When a constant pressure or (TDH) is required, choking this pump back with a Cycle Stop Valve saves more energy than the Variable Speed Pump. Using the affinity law the variable speed only reduced the 10 HP to 7.5 HP. The Cycle Stop Valve simply derated the full speed 10 HP to a 7.0 HP load. |
| Cycle Stop Valves® is a registered trademark. All right reserved unless prior authorization is obtained. Cycle Stop Valves are patented: Patent number 5,988,984 and other patents pending. |
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