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Cycle Stop Valves Technical Info
How Pumps and Motors are Affected by Cycle Stop Valves
Understanding Pressure Differential with CSV
Pump Start Relays and Cycle Stop Valves
Multiple Pressure Settings from a Single Pump System
Multiple Pumps in Parallel
Boosting from One Pump Station to Another
Multiple Pumps in Different Locations with Cycle Stop Valves
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How Pumps and Motors are Affected by Cycle Stop Valves
Back Pressure?
Increasing back pressure does not make pumps work harder. One horse power is the measure of power it takes to lift 33,000 pounds of weight one foot in one minute. Gallons and weight are the same thing to a pump. Restricting the flow from the pump with a valve, back pressure will increase. As back pressure increases, gallons or weight decreases. As the weight or gallons of the water being lifted by the pump decreases, so does power consumption, amps, or horse power. Excess back pressure is a free by-product of horsepower. Back pressure makes pumps pull less amperage not more. Less amperage, means motors run cooler, use less electricity, and last longer.
Minimum Flow?
While Cycle Stop Valves will increase back pressure on pumps when needed, they will never let the back pressure increase to complete shut off head. The Cycle Stop Valve can never completely close. There is always 5 GPM flowing through the valve even when in the fully closed position. This flow is derived from the minimum cooling requirements of a pump and motor. Large submersible motors can operate with much smaller flows than (.5 feet per second). Flow charts for motors running at FULL LOAD AMPERAGE are not relevant for motors pulling an average 60% of full load. As back pressure increases until the pump is only pumping minimum flow, amperage decreases, derating the motor. Pulling only 50 to 60% of full load, the derated motor can safely pump hot water up to 140 degrees according to the charts. If a derated motor can safely pump any amount of 140 degree water, then a tiny amount of cool water (86 degrees or less) will easily prevent the motor from overheating. Minimum cooling charts for derated motors have not been made available by the motor manufacturer. Years of experience has proven many times over that motors such as a 50 HP sub will drop from 77 amps to about 40 amps when the pump is restricted to 5 GPM flow. This 5 GPM flow of 70 degree water going past the motor will increase in temperature to 78 degrees. 78 degrees is not even close to 131 degree water that the charts say can safely cool a 50 HP motor when derated by 40%. Full speed turbines and centrifugal pumps can operate at even lower minimum flows as their motors are cooled by air. Motor and cooling fan are still spinning at full RPM, which will keep a motor that is only pulling 60% of full load amps very cool.
Thrust Bearings?
The load on thrust bearings will increase as the back pressure increases the K factor on the impellers. Bearings in air cooled motors must be properly lubricated and designed strong enough to handle the maximum K factor of the pump. The fan in an air-cooled motor will still be spinning at full RPM which helps to keep the bearings cool. At low flow the power required by the pump is reduced and the windings in the motor produce less heat. With the fan still spinning at full RPM this helps reduce the heat of the entire motor which includes the thrust and radial bearings. With water-cooled motors such as submersibles, heat produced is also reduced because of the low amperage produced at lower flow rates. Less flow is required to cool the thrust bearings as heat from the windings at low flow is reduced, leaving more of the cooling flow available for the bearings.
Radial Deflection?
Radial Deflection increases on centrifugal pumps as the flow rate decreases. The impellers on pumps with a single volute tend to push at odd angles to the cut water vane as flow is decreased. As long as the shaft and radial bearing are strong enough to handle the load, very little if any deflection is possible. Pump companies should not manufacture pumps with shafts that are too slender and bearings too weak to handle this deflection, unless the pump is designed with planned obsolescence as a primary objective. Pumps with a diffuser ring such as submersibles, turbines, and multistage centrifugal pumps, will equally distribute the discharge from the impeller. This makes deflection to any one particular side impossible and radial deflection a non issue.
Resting Pumps and Motors?
Pumps and motors are designed for continuous operation and do not need to “rest”. This means they will last longer if they run continuously than if they “cycle” off and on. Motors that are coasting along at low amperage 24 hours a day, will use less electricity than the same motor pulling full load and cycling on and off every 10 minutes or so. Most motor and pump failures occur during start up. Starting current can be six times normal running amperage. Starting test every component of the pump and motor. Windings, bearings, shafts, impellers, splines, couplings, panels, even the generator at the power company are all tested each time a pump starts. All of these problems go away once the motor is up and running. Common sense would suggest that the fewer times it starts and stops, the longer a motor and pump will last.
Soft Start Equipment?
Cycle Stop Valves will completely eliminate water hammer with or without soft start equipment. The main reason to use soft start equipment is to reduce the end rush of electricity on pump start up. This will reduce the electric bill if a demand charge is included. Some electric companies require soft starts on larger horse power systems. When soft start controls are needed, an auto-transformer type soft start will do an excellent job of reducing end rush currents. These auto-transformer soft starters are mechanical devices that will eliminate the problems associated with troublesome electronic soft starters and variable speed drives.
Cavitation?
Restricting the discharge from a pump with any valve will decrease the NPSH required. The NPSH available will increase as the flow rate decreases. Increasing the NPSHA and/or decreasing the NPSHR reduces the chance of cavitation. Recirculating water from the outlet to the inlet of an impeller can occur at low flow. The 5 GPM bypass exiting the Cycle Stop Valve will keep this recirculating from heating up the pump. Cavitation like wear can occur if the pump chosen has a recirculating problem such as with a loose-fitting wear ring. Pumps that are made of materials with a high tensile strength are more resistant to wear from cavitation. When equipped with an additional pressure sustain pilot the Cycle Stop Valve can also control cavitation at high flow rates by limiting the maximum flow from the pump.
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Understanding Pressure Differential with CSV
Using a Cycle Stop Valve on a large pump with a small pressure tank, the setting of the valve should normally be the same pressure as the pump starts. Using an example of a system that requires 60 PSI constant and a flow rate from 5 GPM to as much as 300 GPM we would do the following.
With centrifugal pumps or flowing wells with a static water level at ground surface, the full deadhead pressure of the pump will be the same as back pressure on the valve.
We determine from our pump curve that our pumps deadhead pressure is 150 PSI. With a Cycle Stop Valve setting of 60 PSI, there is a maximum differential pressure of 90 PSI, which is well below the 125 PSI limit. The Cycle Stop Valve will hold 60 PSI constant on the system. Pressure on the pump case will change from 67 PSI when the system is requiring 300 GPM, to 150 PSI when the flow needed in the system is only 5 GPM. When there is zero flow required in the system the Cycle Stop Valve will allow 5 GPM to fill a pressure tank. Using a tank that has 10 gallons of drawdown, the system pressure will rise to 80 PSI in two minutes, and the pressure switch will shut off the pump. When water is again needed in the system the 10 gallons in the pressure tank will be drained and the pressure will drop to 60 PSI. At 60 PSI the pressure switch will start the pump and the Cycle Stop Valve will hold 60 PSI steady matching the usage in the system.
Higher pressure pumps can be easily controlled using Cycle Stop Valves. Choose a pump that will deliver the maximum flow needed at the required pressure. Pick a Cycle Stop Valve that can handle the max flow and can be adjusted to the pressure required. Find the shut off head for the pump being used and subtract the static water level (if pumping from a well). This will give you the maximum pressure that will be held back by the Cycle Stop Valve. Make sure the Cycle Stop Valve chosen can handle this maximum pressure from the pump. We recommend that the differential pressure through the valve be less than 125 PSI. This means that the maximum pressure that is held back by the valve should not be more than 125 PSI higher than the setting pressure of the valve. If the differential pressure is higher than 125 PSI more than one Cycle Stop Valve may be needed to stair step the pressure down. The first valve would bring this back pressure down from 300 PSI to 175 PSI. The second valve in series would take the 175 PSI and regulate a steady 50 PSI to the system.
Small tanks are not mandatory. Pressure tanks of any size can be used with a Cycle Stop Valve. Tank fill rates can be adjusted and pressure switch band widths can be narrowed. Call the factory if you have any questions.
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Pump Start Relays and Cycle Stop Valves
Irrigation systems with pump start relays can utilize Cycle Stop Valves to vary flow rates to different size zones. Pressure on the irrigation system will remain constant throughout the entire range of the pump. Zones can be matched to the needs of the irrigation and not the pump. This eliminates doubling up on zones when a single small zone is all that is needed.
When used with a pump start relay and in combination with a pressure relief valve the Cycle Stop Valve eliminates the possibility of destroying a pump from dead heading. Many times a pump start relay will start the pump even though varmints or trenching has destroyed the wires going to the zone valves and the sprinklers do not pop up. Set at 60 PSI the internal bypass in the Cycle Stop Valve will allow the pressure to increase to 70 PSI and the pressure relief will dump enough water to keep the pump from overheating.
One of the advantages of pump start relays is that irrigation systems can be made to drain out when not being used to prevent freezing. This can also be a disadvantage in that the system must be refilled to be used. Refilling the system can cause high velocities and water hammer which can be hard on the irrigation system.
Using a Cycle Stop Valve with a small pressure tank and a pressure switch can have some advantages over using a pump start relay. With the pressure switch and tank the entire system stays pressurized. This eliminates water hammer and high velocities which can occur from non pressurized systems such as with the pump start relay. The pressure tank and switch will also allow automatic operation of the pump for using quick connectors, hose bibbs, and garden hoses.
Using Cycle Stop Valves with either a pump start relay or a pressure tank will maintain a constant pressure with any size irrigation zone. This allows precise irrigation and helps preserve our water supplies.
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Multiple Pressure Settings from a Single Pump System
Using a Cycle Stop Valve, a pump or a pumping station can be designed to hold a single constant pressure. In some systems different pressure are required throughout different areas. The pump or station should be designed to operate at the highest pressure required in the system. Anywhere in the system that a line with a lower pressure is required a simple pressure reducing valve can be used.
An example would be a pit mine where the pump station at the bottom might be required to produce 200 PSI. Only 40 PSI may be left for the sprinklers used to wet down the highest road in the pit. On the lower roads the pressure increases as the elevation decreases. The water line at the lowest road is close to the pump station and sees 200 PSI. A simple pressure reducing valve should be used at each of the taps on the way out of the pit. These pressure reducing valves on the water lines at each level can be set at 40 PSI. Each level now has a steady 40 PSI from top to bottom of the pit.
Another example would be a golf course that needs 120 PSI for the main irrigation sprinklers, 50 PSI for the lines at the club house, and 10 PSI for the drip system irrigating the trees on the border. The main pump station is set up for the 120 PSI. The line is tapped at the club house, a pressure reducing valve is installed, and set at 50 PSI. The 120 PSI line is tapped again over by the trees and another pressure reducing valve delivers 10 PSI to the drip system.
Another example would be an irrigation system that uses up to 1,000 GPM at 50 PSI for pop up sprinklers. A small section that needs irrigating is on top of a hill. This section only requires 100 GPM but needs an extra 50 PSI to reach the top of the hill. A small booster pump can be tapped into the main irrigation line going up the hill. This 100 GPM booster pump picks up water from the first pump at 50 PSI and boost it to 100 PSI. This booster would come on at 100 PSI and the Cycle Stop Valve would maintain this 100 PSI with flows from 5 GPM to 100 GPM. When there is zero flow on top of the hill the Cycle Stop Valve on the booster pump allows a small tank to fill to 110 PSI and the booster is shut off. Other small boosters can be added anywhere in the system they are needed. This type system allows the main pump to run at the low pressure that is needed for the majority of the irrigation. When the irrigation is needed at the top of the hill only a small portion of the main flow must be boosted to a higher pressure.
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Multiple Pumps in Parallel
Cycle Stop Valves can solve the problems associated with using multiple pumps in parallel. Most of the time one of the pumps will build slightly higher pressure than the other pump or the static water level in one well is slightly higher than in the other well. This causes the pump that builds the most pressure, even if it is only 1 PSI more, to create a dead head situation for the other pump. At a low flow rate the two pumps are working against each other and the pump that builds the least pressure will be destroyed due to a lack of cooling flow. This is one reason we do not recommend using a single Cycle Stop Valve for two or more pumps unless only one of the pumps is operated at any given time.
When a Cycle Stop Valve is placed on the discharge of each pump before the lines manifold together, back pressure from the second pump does not affect the first pump. Each pump is then working against it's own back pressure. The non closing feature of the Cycle Stop Valve insures a minimum flow to keep each pump cool, because the back pressure or inlet pressure to the Cycle Stop Valve is higher than the outlet or system pressure.
Multiple pumps can be the most efficient way of supplying water. Systems with a wide variation in flow can benefit greatly from being able to utilize the pump or pumps that can best meet the particular flow required. Using a Cycle Stop Valve on each pump allows multiple pumps to operate in parallel safely and efficiently. The following are examples of how Cycle Stop Valves can control different type of multiple pump systems.
Some systems use multiple pumps that are sitting side by side and pumping from the same water source to a common system. Other systems may use multiple pumps located in different locations and pumping from different water sources to a common system. Each pump needs it's own Cycle Stop Valve, check valve, and pressure switch. If the pumps are located in different locations, a small pressure tank is needed for each pump. If the pumps are located together they can use a single pressure tank plumbed to the common discharge of all Cycle Stop Valves. All of the pressure switches should be in a manifold together with the small line that enters the pressure tank. Once installed in this way the only connection between the pumps is that they pump into a common manifold and run on staggered pressure settings.
For this example we will use a three pump system having a small, medium, and a large pump. A minimum of 40 PSI is required at all times and the large pump is set to come on at 40 PSI and off at 50 PSI. The medium pump comes on at 50 PSI and off at 60 PSI. The small pump will come on at 60 PSI and if the system flow ever gets below 5 GPM this pump will shut off at 70 PSI. Usually these large systems have more than 5 GPM leaking so the small pump will run continuously and it's Cycle Stop Valve will hold the system at a constant 60 PSI. The Cycle Stop Valves on multiple pump systems should be adjusted to hold pressure constant at the same pressure as its' pump starts.
When flow increases and the small pump is no longer able to keep up, the pressure will drop from 60 PSI to 50 PSI and the medium pump is started. The Cycle Stop Valve on this pump maintains 50 PSI until flow increases beyond the capabilities of the first two pumps. The pressure then drops to 40 PSI and the large pump is started. The Cycle Stop Valve on the large pump will keep the system pressure at 40 PSI as long as the amount of water needed can be produced by the three pumps. When the system flow is decreased to a point that can be supplied by the small and medium pump, the Cycle Stop Valve on the medium pump will bring the pressure up to 50 PSI and the large pump is shut off. If the system flow continues to decrease to a point that can be supplied by the small pump, the Cycle Stop Valve on the small pump will bring the pressure up to 60 PSI and the medium pump is also shut off. The Cycle Stop Valve on the small pump will maintain 60 PSI supplying the leaks and small demands in the system. Only if there is zero flow will the Cycle Stop Valve on the small pump allow the system to increase to 70 PSI and the small pump is shut off. A pressure relief valve set at 75 PSI can be used for a safety. The largest pump runs at the lowest pressure of 40 PSI, therefore the tank should be precharged with air to 35 PSI.
These pumps can be sitting side by side or they can be miles apart. The staggered pressure settings makes all pumps work together when needed. There is no need for wires or radio controls between pumps. Even pumps that are miles from each other operate on system pressure only. If the pump that is running cannot keep up with the demand, the system pressure drops slightly and the next pump required is started by its' own pressure switch. As demand decreases, system pressure increases and pumps that are no longer needed are shut down by there own pressure switch. Cycle Stop Valves allow simple, safe, and efficient use of multiple pumps in parallel.
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Boosting from One Pump Station to Another
Boosting water from one place to another can be easily controlled using Cycle Stop Valves. Following are a few examples of how to pump in series using Cycle Stop Valves.
#1
A rural water system as an example has 170 miles of pipelines and supplies only 140 connections scattered throughout this distance. Two water wells supply a total of 700 GPM to feed the system. The wells pump a short distance to a storage tank then a duplex pump system draws from this storage and boost to 90 PSI. This booster sends water about 10 miles to another storage tank and booster pump. The second booster sends water another 10 miles to a third storage tank and booster pump system. The process is repeated over and over fourteen times. All along the 170 miles of pipelines there are houses randomly tapped into the line.
An old system used probes to control the level of the storage tanks. When a storage tank was full, a signal would be sent 10 miles upstream to shut off the booster pump. A low probe would send a signal to start the booster. Storage tanks would continually drain and be refilled. A major problem occurs when the booster pumps start or stop. No matter how slow you start the pump or open a control valve, the pressure would spike. Trying to get a ten mile long line of water started could not be done slowly enough to prevent pressure spikes and main line breaks. Then when the storage tank was full, turning off the booster pump would cause a dip in pressure that was followed by another water hammer. These pressure spikes were causing 300 major line breaks each year. Not just a little leak but, ripping out a forty foot section of 8 inch pipe and a roadway.
The Cycle Stop Valve solution was to keep the flow moving. Equipping all pumps with a Cycle Stop Valve means that the usage in the system is continuously matched. The inlet of each storage tanks was also equipped with a special low pressure Cycle Stop Valve. The Cycle Stop Valves on the inlet of the storage tanks close down to a minimum of 5 GPM and are set at 10 PSI. This keeps a constant level of 23' in each storage tank as long as there is a demand for at least 5 GPM. If the system accidently ever went to zero flow, the storage tanks would overflow at the rate of 5 GPM but, the flow would continue to move. The wells now only supply as much water as the entire system is using. Each booster pump now supplies only the amount of flow being used downstream of that booster system. The flow in the system never stops, as the flow rate used in the system is continually matched by the Cycle Stop Valves. Flow rates in the system can vary from as little as 5 GPM to as much as 700 GPM without ever stopping the flow in any of the lines. Taps can be installed anywhere in the system from the discharge of the Cycle Stop Valves on the well pumps to the furthest line past the last booster pump. This continuous matching of the flow completely eliminates the line breaks that occur from frequent starting and stopping of the pumps.
#2
The same system as above can be done without using the storage tanks. Each booster system can draw water directly from the end of the ten mile water line coming from the last booster or well. Simply pick up the water at 20 PSI and boost it back up to 90 PSI sending it on down the next ten miles of pipeline. Each booster system should be fitted with a low suction pressure cut off switch. If there is not at least 10 PSI of pressure feeding the booster then that booster will not be allowed to run. This means of control eliminates the need for the storage tanks that normally feed each booster system. These tanks are not usually large enough to be of any good for storage and are only used as a buffer between the old type booster system controls. Eliminating these tanks will save on purchase cost as well as energy. The pressure feeding each booster pump is the pressure left over from the last ten miles of boosting. Depending on the usage between boosters and the friction loss at least 10 PSI and possible 50 PSI could be left over to feed the next booster pump. Boosting this water from 50 PSI to 90 PSI instead of from atmospheric pressure to 90 PSI saves considerable energy on pumping cost.
Note; Because these type systems run continuously, different size pumps are needed at each booster system to make the system efficient. A small pump can efficiently handle the small demands then a larger pump is only started when needed.
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Multiple Pumps in Different Locations with Cycle Stop Valves
Systems with two or more pumps in different locations can be controlled with Cycle Stop Valves. These are ways of controlling multiple pumps that can be done at the pump locations with a simple pressure switch. There are no wires or radios connecting these pumps together. When the system requires more flow, more pumps come on to supply the need. As flow in the system decreases, pumps go off when they are no longer needed.
#1
An example would be multiple pumps in different location and pumping into a common distribution system. In these systems each pump must have it's own Cycle Stop Valve, check valve, pressure switch, and small pressure tank. The pressure settings can be 5 PSI to 10 PSI between pumps. Adjustments for elevation differences must be made. If one of the pumps is 23' in elevation below another pump, the lower pump will read 10 PSI higher than the other pump. If the lower pump is required to operate the system at 50 PSI, the setting at the pump would be 60 PSI. The opposite would apply for a pump that is higher in elevation than another.
If there are no differences in elevation of the pumps on the system, pressure can be adjusted as follows. Requiring 50 PSI minimum to operate the system the largest pump is set to come on at 50 PSI. That pumps Cycle Stop Valve it set to maintain the 50 PSI and the pressure switch shuts the pump off at 55 PSI. The next smaller pump, which is a mile from the larger pump, is set to come on and the Cycle Stop Valve maintains 55 PSI. When the system pressure increases to 60 PSI this pump is shut off. A third and smaller pump still a distance from the other two pumps set to start at 60 PSI and go off at 65 PSI.
Pressured up to 65 PSI the system is shut off. When water is used anywhere in the system, the pressure drops to 60 PSI starting the smallest pump. The Cycle Stop Valve on the smallest pump is set to maintain 60 PSI. As long as there is 5 GPM being used in the system its' Cycle Stop Valve holds at a steady 60 PSI. When usage in the system increases beyond the capability of the small pump, pressure will decrease to 55 PSI and the second or medium size pump is started. As long as these two pumps can supply the demand, pressure remains at 55 PSI. When more water is required the pressure will drop to 50 PSI starting the third pump. With all three pumps running pressure will remain at 50 PSI as long as demand stays within the combined output of the three pumps.
When the demand decreases to a flow that can be produced by the two smaller pumps, pressure increases to 55 PSI and the third pump is shut off. Decreasing demand until the smallest pump can supply the flow will increase pressure to 60 PSI which shuts off the second pump. If flow can be reduced to zero demand the small pump will slowly fill the system to 65 PSI and the last pump is shut off.
#2
Many pumps can be brought on using 5 PSI to 10 PSI between pumps. When there are even more pumps in the system two ways of setting the pressures are possible. One way is for each pump to have only 3 PSI between on and off. For every 3 PSI drop in the system pressure another pump is started. Pumps can also be brought on in groups. Every time the system pressure drops 5 PSI a group of three or five pumps is started. These two ways of control will work with systems that have ten, twenty, or even more pumps.
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