Some States have very strict rules about requirements for check valves above ground so as to try and eliminate possible negative pressures, which can draw in contamination. However, few people realize that water hammer can be one of the greatest causes of contamination entering a pressurized line. Water hammer causes leaks in underground piping. The negative pressure waves that form before or after the water hammer will draw in dirt and other contaminates through any leaks in the pipe. In this way contamination will be allowed to enter pipelines that were thought to always be pressurized. Water hammer and negative pressure waves are caused by pumps starting and stopping and by variable speed pumps that are slow to react to changes in the flow rate. Cycle Stop Valves react instantaneously to changes in flow, which eliminates negative pressure waves. Cycle Stop Valves only allow pumps to start and stop at the minimum flow rate possible, which completely eliminates water hammer. In this way Cycle Stop Valves can be one of the best tools available to eliminate contamination into pressurized systems. Cycle Stop Valves eliminate contamination made possible by water hammer. This makes Cycle Stop Valves a great benefit to the health of the consumer.
Most Variable Speed Drives do not have water flowing through them and therefore do not require NSF approval. However, variable speed drives send a radio signal to the submersible motor to control the motor speed. This radio signal travels on the skin of the wire instead of the core of the wire as regular AC power does. The pulsing DC voltage created by the variable speed drive, creates voltage spikes, which can make a 240V motor see spikes of 1000V. When these voltage spikes leak through the 600 volt insulation of the down hole wire and motor winding insulation, this stray voltage then travels on the skin of all equipment down hole. This causes a skin effect, which can dissolve metals from down-hole equipment into the water. Skin effect has been known to completely dissolve galvanized bushings and to pit stainless steel and other metals. These metals are then dissolved into the water being consumed. Serious health problems can arise from people consuming these metals that are dissolved into the water by stray voltage from variable speed drives.
Variable speed drives also maintain a constant pressure at all times. This means that water stored in a pressure tank is never exchanged. This allows contamination to grow inside pressure tanks, which can then be forced into the supply system during power outages. When power is restored, this contamination makes its way to the consumer witch can cause more health concerns.
A Cycle Stop Valve also holds a constant pressure as long as there is a certain amount of water usage. However, when the demand is zero or very low, the Cycle Stop Valve allows a pressure tank to fill to a higher pressure and a pressure switch shuts off the pump. When water is again required, the water in the tank is expressed until the pressure drops low enough to restart the pump. This allows the stored water in the tank to be used as needed and the water in the tank does not become stale. The pump does not have to start every time an icemaker is filled or a toothbrush is washed as it does with a variable speed drive.
Some States do not allow for a reduction in tank size when using a constant pressure valve. While this does not hurt anything, this rule does not allow consumers to take full advantage of the constant pressure valve. When the pump is running, water goes past the tank directly to the usage. The only time a tank is helpful is during times when the pump is off and there is intermittent use of water such as icemakers and toilets. As long as some water is being used, the water comes directly from the pump and a larger tank is not useful. As long as the pump is large enough to keep up with peak demands, a large pressure tank is not needed and is a waste of the consumer's money.
Another misconception that many people make is that a variable speed drive saves energy. Head is lost by the square of the pump speed. If we have to lift from a 100' deep well and produce 40 PSI at the surface, then 192 feet of head is always required from the pump. To produce this head a certain amount of RPM must be maintained. As head is lost by the square of the pump speed, small reductions in RPM can make big reductions in available head. This makes it impossible for a variable speed pump to be slowed down enough to save energy when compared to simply throttling a full speed pump with a valve. Many people do not understand that simply choking a pump with a valve will make the pump work easier and use less energy.
Different states and countries handle constant pressure systems differently. Some states, like Florida and Washington are trying to improve the quality and delivery of water to their people. These states have added constant pressure valves to their building codes or design manuals for municipal systems. Consumers in these states are enjoying a constant pressure supply of water, a decrease in cost and footprint of water supply systems, elimination of contamination that goes along with water hammer, and a renewed respect for their state engineers. Other states have been slow to adopt constant pressure systems. These states are wasting taxpayer money on water towers, large pressure tanks, energy, and pump maintenance that could be better put to use on things like schools, roads, and the welfare of the people. Engineers should be educating themselves on new and beneficial innovations instead of sitting back in their comfort zone and continuing to use old technology.