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Michigan DEQ Letter This letter is dated June 15, 2001 and shows that Michigan DEQ is one of the leaders in keeping up with new technology. Many other states are years behind in accepting this new and beneficial technology. This gives me a good opportunity to make a few comments that I have been wanting to make for years about this DEQ letter. #1 "A goal is to duplicate the pressure and flow conditions of municipal water systems." In many ways Constant Pressure Systems give better performance than municipal water systems. Water Hammer from pumps starting and stopping is completely eliminated. System pressure can be even more consistent than municipal water systems. Pressure tanks are smaller which gives a fresher water supply to the tap. Precise pump control means longer service life from pumps and equipment. These aspects of constant pressure control could benefit municipal water systems even more than they benefit domestic water systems. #2 "Benefits of variable speed pumps may include energy savings...." The same reduction in energy use is seen when choking the discharge of a full speed pump with a valve as when slowing the RPM. Variable speed pumps do not save energy when compared to the amp drop from simply restricting a full speed pump with a valve. Even if it were possible for a variable speed pump to save 25% of an average $20.00 per month household electric bill, the $5.00 per month savings would take 16 years to pay for the $1,000.00 added expense of a variable speed control unit. All of the equipment would then have to last for 16 years to pay for itself before any savings in energy is possible. #3 "Benefits of variable speed pumps may include.....an extension of pump and motor life." It is true that softer starting may reduce some stress on the pump and motor. However, higher RPM will increase the wear rate. It is a well known fact of the pump industry that doubling the RPM of a pump will quadruple the wear rate. 3,450 is the standard RPM for small submersible pumps. Many variable speed controls will spin these same pumps at 4,700 to 10,600 RPM which will increase the rate of wear considerably. Many of the variable speed pumps listed in this 2001 DEQ letter have already failed and are longer on the market. Most of the other variable speed pumps listed that are still available have had to undergo several major changes since 2001. The computerized electronic nature of a variable speed controller can also be susceptible to dust, moisture, ambient temperature, and voltage spikes. All of these things combined show why variable speed pumps have not been proven to extend the life of the pump or motor. #4 "The softer start and stop of variable speed pumps reduces water hammer." This is also true. However, the slow reaction time of variable speed controllers can accentuate pressure spikes. When a tap is opened, the pressure will dip low until the controller is able to get the pump up to the required speed. When a tap is closed, the pressure can spike before the controller has time to reduce the speed of the pump. The only way to eliminate these dips and surges in pressure is for the controller to react instantaneously to any changes in demand. Even the fastest of computers takes a second or two to react to inputs. A couple of seconds of the pump running at full speed after the tap is closed will cause a pressure spike. The reason that a pressure tank is used with variable speed pumps is to help smooth out these dips and spikes, not for draw down. Constant Pressure Valves can completely eliminate water hammer as well as pressure spikes and dips. The Constant Pressure Valve gives a mechanical soft start and soft stop. This valve is always in the 1 GPM position when the pump starts or stops. This eliminates check valves from slamming at shut off and pressure spiking on start up. The Constant Pressure Valve is also able to react instantaneously to changes in flow. This keeps the pressure from dipping or surging as flow rates are changing. #5 "With variable speed pumps, the tank provides a small amount of water to prevent the pump from starting for short-term, low-flow demands." Smaller variable speed pumps do not have a pressure band-width between on and off. These variable speed pumps set at 50 PSI will start when the pressure drops to 49.5 PSI and shut down when the pressure reaches 50.5 PSI. Without some distance between on and off pressures, absolutely no water is expressed from the tank before the pump is started. Regardless of the size of tank installed, the pump must start every time the ice maker fills or a tooth brush is washed. Without special provisions to circulate the unused water inside the tank, the water in the tank can even become stale or contaminated. With a Constant Pressure Valve, the valve holds the system at 50 PSI constant as long as any water is being used. When no water is being used, the tank is allowed to fill to 60 PSI before the pump shuts off. When water is again required, the water in the tank is expressed into the system until pressure reaches 40 PSI and the pump is restarted. This allows the full draw down of any size tank to be utilized before the pump is restarted. Utilizing the draw down from a tank is important in that it can eliminate many on and off cycles from small demands such as toilets, ice makers, even leaks and dripping faucets which can be one of the down falls of variable speed pumps. #6 "With pump control valves, backpressurization between the water well and the PCV may exceed the working pressure of the water service line or pitless adapter gaskets..." Back pressure and flow rate are the two things we need to size a pump control valve. Care should always be taken not to exceed the back pressure or differential pressure of the PCV or any component installed before the PCV. Static water level can be subtracted from the amount of back pressure. If the pump builds 155 PSI back pressure, static water level only needs to be 12 feet below the surface to be sure that back pressure on all components stays below 150 PSI. Some Constant Pressure Valves can be installed inside the well casing. Installing the valve in the well before the pitless adapter will still add back pressure to the drop pipe but, eliminates all back pressure from the pitless adapter and underground pipe. #7 "some PCV's contain check valves...." Our Constant Pressure Valve can never completely close and cannot be used as a check valve. A check valve on the pump is mandatory. Check valves can also be installed other places in the system as long as they do not violate any applicable rules or codes. Thank You Cary Austin Cycle Stop Valves, Inc. |
| 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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