Dear Mr. Joseph
This email is in regards to our phone conversation 02-19-09 about the Eston Green Estates well house update. As I explained on the phone, Cycle Stop Valves or CSV's have been used to replace water towers, large pressure tanks, and variable frequency drive pump systems for more than 16 years.
We have not previously pursued approval for use on municipal water systems, as the simplicity of the CSV makes it hard for many people to grasp the concept. Bias favoring VFD over CSV control is based on a lack of knowledge or understanding, as the function of a CSV is in many ways similar to that of VFD controls. The following explanation should help show the many benefits of the CSV over VFD and large pressure tank systems. The citizens of Michigan have a long track record of exceptional service from CSV's on domestic and non-potable water systems. They would appreciate approval to be able to enjoy a reduction in cost and exceptional service from CSV's on their municipal water systems in the State of Michigan.
Basic Operation of CSV
The CSV varies the flow from the pump to match the demand, so standard pressure tank sizing requirements do not apply. Using the 300 GPM pump on the system in question for example, the following scenario applies. Using a 40/60 pressure switch, a 119 gallon bladder tank (30 gal draw down), the CSV is set at 50 PSI. The CSV will maintain 50 PSI constant as the flow required varies from as little as 5 GPM to as much as 300 GPM. Only when the flow rate is less than 5 GPM will the pressure increase to the pump shut off point. While running at 50 PSI the tank is already half full. When no more water is being used, there is always a minimum of 5 GPM flowing through the CSV. This 5 GPM minimum flow is designed to provide adequate cooling for the pump and motor. This 5 GPM minimum flow is also the rate at which the pressure tank will fill, when no more water is being used. In this case it will take 3 minutes to fill the last 15 gallons in the pressure tank, and the pump will be shut off. During this 3 minutes, if someone uses water, the pressure will drop and the pump will continue to run. When the tank has been filling at 5 GPM for 3 minutes, it is safe to say that the demand is low enough to shut the pump off. Since the pump only shuts off when there is basically no demand, 30 gallons of draw down will give ample off time for the pump to cool down before it needs to restart. Run time can be adjusted by the filling of the tank at 5 GPM. With the CSV set at 50 PSI, increasing the pressure switch setting to 50/70 will give 6 minutes of runtime with 30 gallons of draw down. Most pump and motor manufacturers have guidelines for pump run time, off time, and minimum starts per day, and do not specify the size of pressure tank required. With CSV controls, as long as the demand is more than 5 GPM, the pump will run continuously delivering water past, not into, the pressure tank. The only time pressure tank sizing is important is when demand is less than 5 GPM. A worst case scenario would be a continuous and unchanging demand of about 2 GPM. With the controls set as described above, this would cause the pump to run for 5 minutes and be off for 16 minutes, creating a maximum of 68 cycles per day. This can be verified by using the pressure tank sizing and run time calculator at the following link.
As long as demand is more than 5 GPM, the pump will run continuously while the CSV holds a constant 50 PSI. Although the pump continues to run at full RPM, the energy consumed is related to the flow rate, and follows the brake horse power of the pump curve. A linear 40% to 50% drop in horse power can be expected as the flow is reduced from 300 GPM to 5 GPM. It is not necessary to vary the speed, as decreasing power consumption as flow is reduced, is natural characteristic of almost any centrifugal impeller.
CSV Control Variation
Smaller water systems rarely need to vary from the basic CSV control system. When larger flows, multiple pumps, or multiple pressure zones are required, the CSV offers many control options. One of the most common is using various size pumps. For example, a system that requires 300 GPM flow with a 300 GPM back up pump, can benefit from the addition of a 50 GPM pump in the system. The two 300 GPM pumps can be alternated as usual but, the small primary pump is the only one used as long as flow rates stay below 50 GPM. This small pump can be very efficient running continuously as the CSV varies the flow from 5 GPM to 50 GPM. Only when demand exceeds 50 GPM will a small pressure drop trigger one of the larger pumps to start. The CSV on the larger pump varies the flow to add only the extra amount of water being used, so there is no pump cycling. When demand again decreases below 50 GPM, the slight pressure increase from the CSV on the small pump, triggers the large pump to shut off. Multiple pumps can be staggered on in this way to supply as much flow as needed. These multiple pumps can be situated in the same pump house or scattered many miles apart. No wires or radios are needed between pumps, as each pump comes on and off as needed, by simply sensing the pressure.
Another example of a variation in control with a CSV, is to be able to utilize a pressure tank when a small pump is not available. A bypass line around the CSV with a ball valve can control the minimum flow and tank fill rate. As with the 300 GPM pump system, a bypass rate around the CSV of 50 GPM, would allow the pump to run continuously when demand is between 50 GPM and 300 GPM. When demand is less than 50 GPM, the bypass allows a pressure tank to fill and the pump to shut off. Flow rates of less than 50 GPM are met by the pressure tank as the pump slowly cycles on and off. However, we are filling the tank at 50 GPM less the amount of demand, instead of 300 GPM less the rate of demand. This allows the use of a pressure tank that is 1/6th the size and price of a tank normally used with a 300 GPM pump. Cycling is completely eliminated when demand is more than 50 GPM, while flow rates less than 50 GPM cause the pump to cycle slowly and safely.
There are many other possible variations to the basic CSV control scheme, including multiple pumps in the same well, flow based pressure management, pressure boosting applications, and others. The list of different ways a Cycle Stop Valve has been used can be endless. There are a few examples and references at the following link.
There are many advantages to the constant pressure technology of the CSV over large pressure tanks, water towers, and VFD controls. Reducing the RPM with a Variable Frequency Drive or VFD causes a loss of head by the square of the speed. Therefore, a VFD may only be able to reduce power consumption at low flow rates by a couple of percent, over restricting a full speed pump with a valve. The parasitic losses and loss of motor efficiency from a VFD, causes about 5% more power consumption at full flow than when using across the line controls. Using more energy at high flow and slightly less at low flow, the average power consumption when using a VFD is almost exactly the same as across the line with valve control.
VFD systems were introduced in 1968. Many states still have not approved VFD's for public water supplies, as the technical and electronic nature of the VFD is considered unreliable. Not only can there be technical and reliability issues but, many negative side effects are present with VFD controls. Harmonics, voltage spikes, resonance frequencies, bearing currents, and environmental concerns are only a few of the common problems associated with VFD controls.
The CSV has no electronics, which decreases cost, increases dependability, and lengthens the life of pump system components. The CSV was designed to mimic the performance of VFD controls, while eliminating the negative side effects.
It is true that when using water towers or large hydro pneumatic tanks, the pump is always running at it's best efficiency point or BEP. However, it has been documented that the difference in efficiency when using big tanks compared to CSV controls and a small tank, could take from 50 to 100 years to pay off the added expense of the big tank or tower. As the price of these big tanks and towers, as well as maintenance continues to increase, the pay out time also continues to increase.
Although the natural brake horse power of a pump makes it fairly efficient at low flow rates. It has also been documented that using different size pumps (small pump and large pump), can further increase efficiency in systems with large variations in flow rate. This makes it hard to justify the expense of large pressure tanks and water towers. The efficient and reliable control of the CSV, also makes it hard to justify the expense and problems associated with VFD controls. See this link:
Cycling on and off into a large pressure tank or water tower causes transient pressure waves and water hammer as the pump starts and stops at full capacity. These transient pressure waves travel throughout the distribution system from 3,000 to 8,000 feet per second. The water hammer from transient waves causes shockwaves of 10 times the normal line pressure. This can cause major line breaks and/or multiple tiny stress fractures throughout the piping system. These can be expensive and troublesome to repair, as well as wasting tremendous amount of our precious fresh water supply and energy. On average, major line breaks and multiple tiny leaks in the system account for 14% of our fresh water supply being wasted, due to transients and water hammer.
On smaller systems there are times when no water is being used. The CSV gives a mechanical soft start and soft stop. When water is demanded, the small pressure tank supplies water instantaneously. The CSV then lets the pump start at either 1 GPM or 5 GPM, and there is a smooth transition between water coming from the pressure tank, as the CSV quickly opens up to supply exactly the amount of water being used.
On larger systems the flow never completely stops, it is just varied from a little to a lot, according to demand. One of the first laws of physics we learn, is that a body in motion wants to stay in motion, and a body at rest wants to stay at rest. A constant pressure system varies the flow rate to keep the water in motion, which completely eliminates transients and stress on the piping system.
The pressure spikes and water hammer from pumps cycling into large hydro tanks and water towers can be easily seen as a heart beat on pressure recording charts. Constant pressure controls vary the pump output to match the demand. This eliminates heart beat pressure spikes by keeping the pump from cycling on and off. Even electronic soft starts and soft stops do not eliminate water hammer. Head is increased by the square of the pump speed, so the first 90% of pump speed does not produce flow. Only the last 10% of pump speed produces enough pressure to push open the check valve and initiate flow. With a soft starter, the last 10% of pump speed happens too fast to prevent water hammer. The same problem occurs with electronic soft stops as well.
Cycle Stop Valves react to changes in pressure and flow instantaneously. A slight increase in pressure directly and instantly changes the position of the valve inside the CSV. This means that a slight increase in pressure is instantly met with a decrease in flow rate, and a slight decrease in pressure is instantly met with an increase in flow rate. The non-closing feature of the Cycle Stop Valve allows for extremely fast valve travel. Since the CSV can never completely close, slamming the valve shut does not cause a dead end in the pipe line for transient pressure waves to bounce off of. The non-closing or "notched" seat in the CSV allows for some flow, even when the valve is in the fully closed position. The small flow through the notched seat equalizes pressure, and eliminates the negative pressure wave that normally follows a valve closure. Before the valve opens, some flow is already flowing through the notch, so quickly opening a CSV does not cause a surge of pressure that would normally initiate a transient pressure wave in other fully closing type valves. Response time of the pump control system is crucial in eliminating transient pressure waves in a pipeline. The non-closing feature of the CSV is also crucial, allowing for valve response times that are almost immediate.
The same increase in pressure that causes an immediate reaction in the CSV, causes a much slower reaction by a VFD. The increased pressure pushes on the pressure transducer. The pressure transducer decreases the 4 to 20 milliamp signal to the VFD. The VFD decreases the frequency to the motor. Then the motor starts slowing down to produce less flow. Even if all this happens in less than a second, transient pressure waves traveling between 3,000 and 8,000 feet per second, have ample time to wreck havoc on the pipeline. While response time can be adjusted in many VFD's, the shorter the programmed response time, the more "hunting" or pressure bouncing is seen in the pipe line. The slightest delay in the response of the pump control such as a VFD, can exacerbate transient pressure waves, which cause destructive water hammer.
The squirrel cage induction motor and centrifugal pump are two of the longest lasting and most dependable pieces of equipment in use today. Running on the standard sinusoidal power, there is a slow rate of voltage rise, and no voltage spikes to the motor. Reducing the flow rate with a CSV causes a natural reduction of amperage which de-rates the motor. De-rating the motor produces less heat, and requires less flow for cooling purposes. The pump and motor never go through destructive critical speeds or resonance frequencies, when the unit is always spinning at full RPM. The CSV allows the pump to produce full flow and pressure when needed, and simply works the pump back to a minimum safe flow, when less flow is required by the user.
A VFD uses standard sinusoidal power to charge a capacitor bank. The VFD then pulses this DC current to simulate AC power. The quick DC pulses causes a rapid rate of voltage rise that is extremely hard on motor windings. This pulsing also causes the voltage to overshoot, and can cause voltage spikes to the motor that are 400% higher than the fundamental voltage. The frequencies generated by the VFD causes "harmonics" or "dirty power". This "dirty power" is overlain on the fundamental power, which causes excess heat and less efficiency from the motor. The odd order harmonics are not canceled out, and end up going back into the electrical grid. This can cause other equipment on the same electric grid to be less efficient, and can disturb any other equipment effected by radio signals. Line and load filters, as well as VFD's with an active front end can help alleviate harmonics but, they cannot completely eliminate them. Filters also generate heat which requires additional cooling and waste energy. The "stray voltage" created by VFD's also negatively effects cattle and other animals. This has been proven to cause reduction in milk production, mastitis of the udder, and stillborn calves, among other things. Although less studied and documented, there is no reason to believe that these same problems would not affect humans as well.
Every component in a pump and motor has a resonance frequency. Varying the speed from zero to full speed with a VFD causes every component to vibrate, as the unit goes through the resonance frequency of every particular component. The VFD itself also has heat losses which reduces efficiency. When a VFD manufacturer says it's VFD is 96% efficient, that means it is losing 4% of the available power before it ever gets to the motor. These VFD "parasitic losses" cause a pump controlled by a VFD, to use more power than across the line controls, when running at maximum capacity. The VFD also causes an electrical current to run on the motor rotor and discharge through the ball bearings. These currents cause electrical fluting of the bearings, which looks like welding damage and causes premature failure of the bearing races.
The CSV never varies the RPM of the motor. Therefore the unit never runs at any critical speeds or resonance frequencies. With across the line controls, 100% of the power gets to the motor. There are no harmonics generated to cause "dirty power", bearing currents, or all the problems they associated with VFD controls.
Differences in Motor Cooling
With pressure tanks and water towers the pump is always running at full flow, and minimum flow required for motor cooling is not a problem. With VFD controls, the water flow rate past a submersible motor, and the air flow rate through an above ground type motor, are critical in maintaining proper cooling for the motor. With VFD controls the motor actually requires more cooling as the harmonic frequencies generate additional heat. When a motor is slowed down to produce less flow, the VFD requires less motor horse power from a larger motor. The VFD controlled motor still requires the maximum amount of cooling flow. With an air cooled motor the fan is now spinning slower as well, and in many applications an additional fan must be used to provide adequate cooling for the motor. With a VFD controlling a submersible motor, the standard 1/2 foot per second flow, as with motors running at maximum service factor amps, must be maintained to properly cool the motor. In the case of a 6" motor installed in an 8" casing, 45 GPM minimum flow must be maintained at all times. This means a VFD can vary the flow from a 300 GPM pump to as low as 45 GPM. When flow rates are less than 45 GPM, additional equipment and controls such as large pressure tanks must be implemented to safely handle the demand.
At low flow rates, the CSV reduces the amp draw of the motor, yet the fan in an air cooled motor is still spinning at full RPM. This provides more than adequate cooling for the motor at low flow rates. With a submersible motor, the CSV derates the motor by decreasing the amp draw. A derated submersible motor can be adequately cooled even when pumping hot water, so very little cool well water is required for proper motor cooling. The same 300 GPM pump and motor that requires a minimum of 45 GPM to be properly cooled when controlled by a VFD, only requires 5 GPM for proper cooling when controlled with a CSV.
CSV's come in a variety of models and sizes. Some small CSV's are made of PCV, while others are made of a low lead allow. Larger models are made of all 18-8 stainless steel, while others are coated inside and out with an FDA approved coating. All CSV's conform to NSF 61 standards but, are not NSF certified, as certification is expensive and would only further increase cost to the end user and tax payer.
Reliability and Dependability
Again, the squirrel cage induction motor and centrifugal pump are two of the longest lasting and most dependable pieces of equipment in use today. Cycle Stop Valves have already proven to more than triple the life of pumps, motors, and system components. Adding the problems of VFD controls can drastically reduce the life span of pumping equipment. There are many good uses for VFD controls where they are not marginal-ized for losing head by the square of the speed. VFD's have an accumulative effect on harmonics and stray voltage. The more VFD's in an area, the worse the problems. Eliminating VFD's on high power pumping installations, where control can easily be accomplished in other ways, increases the life of the equipment and reduces the effects of stray voltage on the surroundings. Even though VFD's have become much less expensive, the decrease in pump equipment life and the short life expectancy of the VFD itself can drastically increase total cost in the long run.
Many CSV's have been used for municipal water supply, but most CSV systems have been installed on domestic or non-potable water systems. There are hundreds of thousands of CSV systems working with an exceptional track record for energy savings, cost savings, and system reliability. As the manufacturer, we do not usually know where these systems have been installed but, many of them are in the state of Michigan. It should be easy to see the benefits when looking at the long track record for Cycle Stop Valves on domestic and non-potable water systems. Pumps make no distinction in providing water to people, plants, or animals. Therefore, it should be understood that the same system that has proven to be dependable and efficient providing water to domestic systems, irrigation systems, animals, and industrial plants for many years, will be just as dependable and efficient providing water for the people.
Some states and other countries have long ago seen the benefits of using CSV controls, and have approved the CSV, without request from Cycle Stop Valves, Inc.
As guardians of the public trust, public officials should now more than ever seek out new and innovative technology, such as the Cycle Stop Valve, to decrease costs, increase efficiency, and extend the life of water system components. Although the explanation may be complicated, the actual function of a Cycle Stop Valve is the ultimate in simplicity. Leonardo DeVinci once said, "simplicity is the ultimate sophistication".