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Home / Technical Information / FAQ- Requenctly Asked Questions / Domestic System FAQ

Domestic System FAQ

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In a closed, automatic water system a pressure tank is used to store water and maintain system pressure between specified limits (such as 30 to 50 PSI). As the water level in the tank rises, tank air is compressed in the upper part of the tank until the upper pressure limit is reached (i.e., 50 PSI). At this "cut-out" point a pressure switch opens the electrical circuit to the motor and the pump stops. The compressed air in the tank acts like a spring pushing down on the water to create system pressure. When a valve is opened in the water system, the air pressure in the upper part of the tank forces water to flow out of the tank and into the system. As the water is drawn from the tank, the air occupies a larger space and the pressure drops until the lower limit is reached (i.e., 30 PSI), At this cut-in point the pressure switch closes the electrical circuit to the motor and the pump starts. A cycle is thereby completed.
The basic components are: a well, or other water source; a pump to move the water from the well into the house; a pressure storage tank to provide automatic operation of the home water system
Check valve or foot valve; suction and discharge pressure gauges, pressure relief valve; suction and discharge isolation valves, interconnecting piping and wiring.
Wells can be drilled, driven or dug. They can be shallow (less than 25 feet) or deep (more than 25 feet). Other water sources include cisterns, and surface water, such as a spring, lake, or other surface water.
Pumps located above ground are known as Jet Pumps. They can be shallow well jet pumps or deep well jet pumps. Pumps submerged in the water source are known as Submersible Pumps. They can be used in shallow or deep wells. Submersible pumps are the most popular sold today.
The most popular tank sold today is the "sealed diaphragm" or "captive air" type tank, where water and air are permanently separated by a sealed diaphragm. Other types of tanks include conventional galvanized tanks, and floating disk type tanks.
Years ago, the most common tanks were galvanized or glass lined and had no separation between air and water. Since air dissolves in water, these tanks required constant draining and air pumping to prevent them from becoming water logged -- that is, full of water with no air left. Water is virtually incompressible and a water-logged tank will hold perhaps an ounce of water between 30 and 50 PSI. The result is a pump that "telegraphs" or cycles rapidly, leading to premature motor failure. Some attempt was made in the past to solve this problem by inserting a round float in the tank to act as a barrier between the air and water. This was successful in slowing down the dissolution of the air. But, the more satisfactory solution was achieved with the introduction of the captive air bladder tank or "pressure tank".
To maintain the proper air pressure inside the atmospheric tank, a special valve, called an air volume control, is mounted to the tank at the level where the water will be when the pump starts.
The diaphragm and bladder type tanks use a mechanically locked-in flexible separator, which completely isolates the air from the water. The tank is precharged at the factory and has an air charging valve installed on the top of the tank to allow the installer to change the pressure in the field to accommodate different system pressures. Precharge of metal bladder of diaphragm tanks: 2 PSI less than pressure switch cut-in pressure. Example: Switch set 30-50 PSI,,,,,, metal tank precharge 28 PSI Precharge of fiberglass bladder of diaphragm tanks: 4 PSI less than pressure switch cut-in pressure. Example: Switch set 30-50 PSI ...fiberglass tank precharge 26 PSI
The Air Volume Control is mounted on the tank about 1/2 way up the tank. A 1/4" tubing is connected from the Air Volume Control to the suction of the pump. When the pump starts, the diaphragm in the Air Volume Control is drawn to the right by pump suction. Air enters through the snifter valve, if water level in tank is above connection to the air control. When the pump stops, the pressure equalizes, and the diaphragm moves to the left by spring pressure and forces air into the tank. The DRAWDOWN of an atmospheric tank is only 10% when the pressure is set 30PSI cut-in 50 PSI cut-out. EXAMPLE: 8.2 Gallons (10% of 82)can be drawn from an 82 gallon atmospheric tank before the pressure drops from 50 PSI to 30 PSI
Different plumbing systems have different needs. Some fixtures require high pressure without much flow, while others need maximum GPM at a reasonable pressure to operate sufficiently. A pump will produce less flow as pressure increases and vice versa. Keeping this in mind adjust the pressure switch accordingly. Use lower settings where a high volume of water is necessary (i.e. sprinkler systems), and use higher settings where pressure is key (dishwashers, flush valves, etc.)
It is possible to store an added volume of water beyond the standard tank drawdown (known as supplementary drawdown). By setting the tank pressure below the pump cut-in setting, a reserve of water will be left in the tank during every cycle. This will help in peak flow situations, where demand exceeds pump output. It's also useful during power outages, when extra storage can mean a few gallons of drinking water or another toilet flush. Use the Acceptance Factor Chart to determine how much water will be stored. The tank precharge now becomes the cut-in axis on the chart. Be careful not to exceed tank manufacturers' maximum acceptance factor to avoid damaging the internal water reservoir.
In some applications, the standard 20 PSI differential between pump cut-in and cut-out is too great. This fluctuation can be an annoyance in pressure-sensitive plumbing systems. By narrowing the differential, a tighter pressure range will result. You must ensure that the tank will still store enough volume to prevent pump damage. A lower overall setting may be necessary.
Pump motor life can be measured in cycles-starts and stops. A tank should be large enough to prevent a pump from overheating due to rapid cycling. Selecting a tank suitable for a given pump application is accomplished by knowing the minimum run time, pump GPM and system operating pressure. As an example, a 1 HP pump with an output of 15 GPM. has a 1 minute recommended minimum run time between start and stop cycles. To run a 15 GPM pump for 1 minute, 15 gallons of water must be pumped and stored (15 GPM X 1 = 15 gallons). This storage volume is referred to as drawdown, and is the usable water between pump cycles. Next, it is necessary to determine what total tank volume (water and air) is necessary to store 15 gallons. This number will change depending on pump cut-in and cut-out pressures. As these numbers increase, the storage capacity of the tank decreases. An Acceptance Factors Chart shows that a 30/50 PSI pressure setting will yield a 31% drawdown, where a 40/60 PSI setting allows only 27%. For our example we'll use a 40/60 setting. Dividing the 15 gallons of stored water by the .27 Acceptance factor results in a total tank volume of 56 gallons necessary to properly protect this particular pump. Select the tank size closest to this figure.
When water flows through piping, it creates friction, which in turn decreases flow. It is necessary to mount the tank and pressure switch in a location that minimizes pressure drop and allows flow and pressure to balance. Essentially, pipe the components in a location that allows each to see an equal pressure at any given time. In a single-tank system, this means keep the pressure switch and tank as close as possible (within 4 feet). If this can't be accomplished, adjust the pressure switch accordingly to account for the added pressure drop through the piping between it and the tank. Tanks can be mounted in parallel for added capacity and drawdown. For multiple tank installations (click on top illustration) use basic geometry to locate the tanks equidistant from each other in order to balance flow pressure. Avoid placing tanks in series in the same line. Rather, use a manifold setup to allow multiple tanks to act as one. Then, locate the pressure switch at the beginning of the manifold, or equally spaced between the tanks. Following these guidelines will ensure each tank is used to its maximum.
A water well pump delivers water from a well or other water source to a tank where it is held under pressure until needed in the system. Water well pumps are modified centrifugal pumps. An IMPELLER rotating on a motor shaft, forces water across the vanes (or blades). The water picks up speed, lowering the pressure in the center of the impeller. This creates a vacuum, sucking in more water. Meanwhile, a DIFFUSER receives the water that has been forced to the outside of the impeller, and slows it down, thus increasing the water pressure. The water is then passed into a discharge pipe. Because straight centrifugal pumps are not practical for real world water well applications (they can only lift water about 16 feet) they need to be modified for water well use. There are two ways to do this: Add a jet assembly. (jet pumps) ; Add multiple impeller/diffuser combinations. (Submersible pump.)
A typical JET ASSEMBLY has a NOZZLE which forces water through a suction chamber to create a vacuum, permitting atmospheric pressure to force water into the suction chamber. And a VENTURI, or DIFFSER, which converts the velocity of the water into pressure.
The impeller and diffuser of a submersible pump are positioned in a bowl. The combination of impeller, diffuser and bowl is called a STAGE. Multiple stages increase the performance of the pump, using as many stages as necessary to satisfy capacity and pressure requirements.
If all domestic water supplies were delivered by gravity, we wouldn't need pumps. However, the level of the water is almost always below the ground, as well as below the level of the house we need to serve. It may be just a few feet away, in a spring, lake or pond, or in a shallow well. Just as often it may be hundreds of feet beneath the surface, in an underground chamber or "aquifer." In order to make the water "flow uphill", we use a pump. If the pump is immersed in the water supply, our problem is somewhat simplified. But what if our pump is above the ground? How do we get the water up into the pump? We use a force called suction. Suction is created when pressure forces something into a vacuum. The textbook definition of a vacuum is a space where there is no matter; no air, no molecules, no anything! But this is a "perfect" vacuum, rarely found except in outer space or the laboratory. A more practical definition of a vacuum is: a space where the pressure is significantly below atmospheric pressure. Now, if suction is created when pressure forces something into a vacuum, where does this pressure come from? It's atmospheric pressure. The atmosphere all around us has weight. It exerts a pressure of 14.7 pounds per square inch (PSI) at sea level. So here's how a pump at ground level can raise water from a source beneath it. First, the vacuum chamber (or suction chamber)of the pump is piped down into the water source. Atmospheric pressure is removed from the chamber, creating a partial vacuum. This allows the atmospheric pressure on the surface of the water source to force the water up the pipe and into the vacuum chamber of the pump. And that's how we use suction to make water flow uphill.
Under ideal conditions, one pound per square inch (PSI) of pressure will raise water 2.31 feet in a pipe. Therefore, at sea level, atmospheric pressure (14.7 PSI) should create enough force to raise water almost 34 feet. ( 14.7 PSI x 2.31 Ft.+ 33.957 Ft.) However this assumes a perfect vacuum. This, as we know, never happens in real life. In real life, there is also friction between the water and the inside of the pipe. For all practical purposes, atmospheric pressure will raise water 25 feet. (Even less at higher elevations where atmospheric pressure decreases). The height of the water that can be raised is reduced by one foot for every 100 feet of elevation. At 5000 feet, water can only be raised 20 feet.) Note: Since it takes a certain amount of pressure to raise water to a height in feet, there is a relationship between pressure and feet (sometimes expressed as "feet head")
To convert pressure to feet: multiply by 2.31
To convert feet to pressure: multiply by 0.433 or divide by 2.31.
Try to suck soda from a bottle by closing your mouth over the neck of the bottle. It can't be done. Now use a straw. It's easy! You've created a partial vacuum in your mouth, allowing the atmospheric pressure on the surface of the soda, inside the bottle, to push the liquid up the straw and into your mouth.
As water flows through a pipe on the way from the well to the home, the inside of the pipe resists the free flow of the water. This resistance is called "friction". Friction means extra work for the pump because it has to work harder to move the same volume of water. Therefore the term friction loss. Friction loss works against pump performance, so you want to keep it as low as possible.
Friction loss is affected by these three factors: Friction loss INCREASES as pipe length increases. The longer the pipe, the more the friction loss. Friction loss INCREASES as flow rate increase. The greater the flow rates the more friction loss. Friction loss DECREASES as the inside pipe diameter increases. The larger the inside diameter of the pipe, the less the friction loss, Therefore, you can reduce friction loss by using a larger inside diameter pipe. Note: Friction loss between the tank and the upstairs outlet in the average home is 3 psi (6.93 feet).
In addition to overcoming friction loss, the pump must raise the water vertically from the water source to the highest outlet in the home. We use the terms vertical lift and vertical elevation to describe this process.
When the pump located above the ground (Jet Pumps), vertical lift is the distance from the pumping level in the well to the centerline of the pump suction. Vertical elevation is the distance from the pump to the highest outlet in the home. Notice that for jet pumps, vertical lift is on the suction side of the system. Vertical elevation is on the discharge side of the system, or between the pump and the home
When the pump is submerged in the water, there is no suction side in the system, only a discharge side. We simply total the distance from the pumping level in the well to the highest outlet in the home and call it vertical elevation.
The water system should have enough capacity to satisfy the family needs, particularly during periods of heaviest demand. The amount of water needed depends in three factors: Number of people; Number of fixtures in the home; Peak demand Periods
Peak demand periods usually occur during morning and evening hours when most or all of the family is at home and the demand of water is the heaviest. These are the times when the most outlets are being used at the same time. Peak demand periods usually involve 7 to 10 minutes of maximum water usage (showers, dishwasher, etc)
To make sure your system will provide adequate capacity, you can use either or both of these methods: Fixture Method: One gallon for every fixture in the home or a Seven Minute Peak Demand Method:
Use one gallon for every fixture (outlet) in the house.
You assign a value based on the bathrooms in the house: 1 bathroom in the home 7 GPM; 1-1/2 bathrooms in the house 10 GPM; 2 to 2-1/2 bathrooms in the house 14 GPM ; 3 to 4 bathrooms in the house 17 GPM; 5-6 bathrooms in the house 21 GPM. Values given are average and do not include higher or lower extremes Peak demand can occur several times during the morning and evening hours. Additional requirements: farm, irrigation and sprinkling are not shown, These values must be added to the peak demand figures if usage will occur during normal demand periods.
In addition to enough capacity, there must also be enough pressure to properly service the home. Discharge pressure is made up of: Vertical Elevation: The pressure needed to raise the water vertically from the pumping level to the highest outlet in the home. (Measured in feet. Convert to PSI) PLUS Friction loss: The Friction loss in all pipe and fitting between the tank and the outlet. (Expressed in PSI) PLUS Service pressure. Pressure required at the outlets (Expressed in PSI)
The most commonly used Discharge Pressure is 30/50 PSI. This means that the pump will cut-in when the pressure in the system falls to 30 PSI. And cut-out when the pressure reaches 50 PSI. This provides enough pressure to service most homes adequately. When selecting a pump, always use the lower or cut-in pressure, because that represents Peak Demand conditions. Pressure switches are adjustable in the field to accommodate unusual conditions. For example. An older home with corroded pipes and fittings or rusty fixtures may require extra pressure to overcome the additional friction loss caused by these conditions. Increased discharge pressure may also be required if vertical elevation is greater than normal; for example, a three story home or a home located a great distance from the pump.
Some of the factors involved in selecting which type of pump to use include: Replacement situation (kind of pump is being replaced); Maximum pumping depth; Well diameter Judgment, experience and customer preference will also play a part in the final pump type selection. Other factors could be cost, future water usage projections and cost and ease of service.
Shallow well Jet Pumps are used to depths to 25 feet. They are installed outside of and above the well. The jet assembly is integral with or bolted to the pump and a suction pipe extends to below the water level in the well. They are called SHALLOW WELL JETS because they have a maximum pumping depth of 25 feet. They depend entirely on atmospheric pressure to force water into the suction chamber of the pump. Shallow Well Jets are designed to operate on 1-1/4" or larger wells.
Deep well jet pumps are used to depth of 230 feet. The DEEP WELL JET PUMP differs from the Shallow Well Jet in that the jet assembly extends down inside the well, making greater pumping depths possible. They operate at pumping depths up to 230 feet. Deep Well Jets require a FOOT VALVE below the jet assembly in the well to prevent water from running out the bottom when the pump is stopped. This maintains pressure in the system and allows the pump retain its prime.
There are two configurations of deep well jet pumps: a Twin Pipe and Packer type deep well system
The deep well twin pipe system has two pipes extending down into the well; a PRESSURE PIPE to carry DRIVE WATER down to the jet assembly in the well. And a SUCTION PIPE to deliver the upward pressure to the jet pumps. Twin Pipe deep well jet pumps require a 4" or larger well casing.
The Packer Type Deep Well Jet has only a single suction pipe extending down into the well. Pressure is created by water flowing down between the well casing and the suction pipe. A special well casing adapter is required to connect the top pipes to the packer pipe. Packer Type Deep Well Jets are designed for 2” and 3” well casing.
Submersible well pumps are used in depths up to 1100 feet or more. Submersible Pumps get their name because the entire unit, including both pump and motor, are submerged in the well during operation. They are powered by dependable 2 or 3 wire Submersible motors. A Submersible Pump works by passing water up through a series of STAGES, each stage consisting of an IMPELLER, a DIFFUSER and the BOWL in which they are seated. The width of the impeller determines pump capacity (GPM). The diameter determines pressure PSI. The number of stages in a submersible pump determines how high the pump will push the water.
Submersible pumps offer a number of advantages to the homeowner: Greater pumping depth; Higher Capacity and Pressure; Greater Efficiency. All the water pumped by the well is delivered to the service outlets. This reduces power consumption and lowers operating costs.

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