CSV vs Tankless Pump Controls
A small leak such as a dripping faucet or running toilet can also cause the Davey to cycle on and off multiple times, until the motor is shot. A standard jet pump with a small tank and pressure switch are a much better option. Adding a Cycle Stop Valve delivers constant pressure and makes the system cycle less, and be much more reliable. Several distributors are now using our Pside-kick pump control kit on regular jet pumps instead of the Davey.
The CSV can only deliver constant pressure when the pump is running. When the pump is off, the tank delivers the flow and pressure. It is the long term uses such as watering the lawn or filling the pool that causes excessive cycling. In these cases a pump with a standard pressure tank setup may cycle every 2 minutes, which is 30 times an hour, 720 times per day, 262,800 times per year, and so on. This is where the cycling becomes destructive and shortens the life of the pump and system. All this cycling goes away with the use of a Cycle Stop Valve, and the pump system will last many times longer.
A pressure tank only system may only cycle about 3 times while showering or washing cloths. This does not cause enough cycling to be destructive, but the continuous 40 to 60, 60 to 40 cycling can be aggravating in the shower, and can cause tankless water heaters not to stay on as they should. For showers and laundry, the CSV makes the washing machine fill faster, delivers enjoyable constant pressure for showers, and keeps an instant water heater working because of the steady flow.
For intermittent uses of water such as flushing toilets, icemakers, washing toothbrushes, etc., utilizing the water in a pressure tank is a good thing. All 9.3 gallons in your pressure tank can be utilized before the pump must start. This allows you to flush about 5 times, or the icemaker to work for a month before the pump must start. Of course you will see the pressure drop from 60 to 40 as the water in the tank is used, which is the only way you can get water from a pressure tank. Once the tank is empty and the pump has started, the CSV will hold your system at 57 PSI as long as water is being used.
Narrowing the bandwidth of the pressure tank or using a much smaller tank can reduce the time waiting for the pump to start. Although the more narrow the pressure switch bandwidth or the smaller the tank, the more often the pump must run for intermittent uses such as toilets and ice makers. Even with a 4.4 gallon size tank that only holds 1 gallon of water, you get to use the whole gallon before the pump starts, which helps with toothbrush washing and ice makers. With a small tank like this, the pressure drop from 60 to 40 happens before you get the temperature adjusted in the shower, and you never notice anything but "constant pressure". With a larger tank, you may notice a drop in shower pressure when you first start but, the pressure will become constant as soon as the pump starts.
Not being able to utilize any water from a pressure tank is one of the many downfalls of the so called "constant pressure pumps" (VFD), or "tankless" controls such as the Davey or Masscontrol. When a pump system is set to maintain exactly 50 PSI all the time, you never put any water in a tank or get any out. This means that the pump must start every time you wash a toothbrush, no matter how large of a pressure tank you have. It also means that a small leak such as a slowly dripping faucet or a toilet running that you can't see, will cause the pump to cycle many thousands of times. Some of these "tankless" or "constant pressure pumps" have about an 8 second delay built in. So a slight drip anywhere can cause the pump to cycle every 8 seconds, 24 hours a day, which is 8,550 cycles per day, or over 3 million cycles per year, which a pump can never survive.
Conclusion: Constant pressure for long term uses of water is a good thing. Being able to utilize the water in a pressure tank for short term uses of water is a good thing. The Cycle Stop Valve is the only "constant pressure" device that delivers both. This is only one of the many reasons why Cycle Stop Valves are superior to "constant pressure pumps", VFD's, or any of the "tankless" controls that are available.
Flow Switch or Shuttle Valves
The functions of a Flow Switch or Shuttle Valve are to:
- Start the pump when flow is being used
- Stop the pump when no flow is being used
Selecting a Flow Switch or Shuttle Valve
When selecting a Flow Switch or Shuttle Valve, certain information must be known:
- System pressure required
- Pump capacity
- Maximum output pressure of the pump
A flow switch is designed to maintain power to the pump until the flow rate has dropped very low, (usually less than 1/2 of a GPM). When flow is less than 1/2 GPM, the flow switch falls to the normal position, and opens the circuit to shut off power to the motor. A very small pressure tank may be used with these type controls. When the pump is off, flow required may be so low, that the flow rate from the pressure tank, if there is one, is not sufficient to raise the flow switch to start the pump. Therefore, most of these type systems use low pressure to restart the pump. The pump is stopped when the flow rate is low enough to let the flow switch drop. Then the pump is restarted when the pressure drops to a predetermined lower pressure setting. These systems can best be described as pressure on, and flow off.
A shuttle valve works on the same principle as a flow switch. The shuttle part of the valve is controlled by the flow. When there is more than 1/2 GPM flow, the shuttle moves to block pressure to a standard pressure switch. This keeps the pump running, even though the pressure produced by the pump may be more than the pressure switch shut off pressure. Only a reduction in the amount of water being used (usually less than 1/2 of a GPM) will cause the shuttle valve to move to the normal position, and open the inlet to the pressure switch. The pump discharge pressure is already more than the off setting of the pressure switch, so power to the pump is quickly shut off. When water is again required, the pressure switch can then restart the pump at a predetermined lower pressure, as with any pressure switch controlled system.
With a flow switch or a shuttle valve, once the pump is started, the pressure produced, and the energy consumed, is determined by the capabilities of the pump and the amount of flow being used. At low flow rates the pump builds more pressure, draws less amperage, yet still uses more energy per gallon. At high flow rates the pump can build less pressure, draws more amperage, yet uses less energy per gallon. The pressure to the system varies with the pump curve. For this reason, these devices are normally used with pumps that cannot build more pressure than the system can withstand. The flow switch or shuttle valve does not control pressure, so the maximum pressure the pump can build will be applied to the entire water delivery system. In some cases, a Pressure Reducing Valve or PRV is used in conjunction with these devices. Technical concerns and differences in the types of these controllers require that you follow the actual manufacturers guidelines for selection and installation.