 |
|
|
Number of Starts Per Day When Using Variable Speed Pumps When using a variable speed pump for a small demand or leak of ½ of a GPM the pump will ramp up and down continuously. Maintaining a constant pressure of 50 PSI all of the time will not allow any water to enter a tank or be expressed from a tank. There must be a bandwidth between the start and stop pressures to allow a tank to be used. It does not matter if the tank is a 1 gallon size or 10,000 gallons, holding 50 PSI constant, the pump will still have to start every time someone washes a tooth brush. Every time the ice maker fills the pump must start and stop. Even though variable speed pumps do not have mechanical switches, the motor must be energized and de energized with every small demand of water. A pressure tank will help reduce pressure spikes that occur when the pump is not slowed down as fast as the tap was closed off. A tank will also help to keep the pressure from falling low while waiting for the pump to speed up to supply a demand. A pressure tank will help with the quick dips and surges in pressure but is not allowed to use it's drawdown for small demands. This not only causes the pump and motor to start and stop hundreds of times per day but also leaves the water in a tank to stagnate. The slower the reaction speed of the variable speed pump the more dramatic the dips and surges in pressure. Ramping up and down slowly enough to prevent water hammer may also cause the submersible motor to operate too long below 30 hertz. Operating below 30 hertz does not give the hydroplane effect needed to properly lubricate the thrust bearing. This lack of lubrication can cause the destruction of the thrust bearing. Slow ramping up of the motor can also lock up the pump if any sand or debris is present. Some variable speed pumps have a reversing feature to try and unlock the impellers that are stuck with sand. Even if this reversing feature does free up the impellers and get the pump started, the end user is still standing in the shower with soap in his hair waiting on water. This is because the small tank used with variable speed pumps has long been empty waiting on the pump to start. |
| 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. |
|
 |
||||