Water Pumps & Pressure Systems
Hitchon's Pump House Explains a Variety of Water Pumps & Pressure Systems
Sources of Water
A source of water or a well is often referred to as shallow or deep. These terms are referring to the depth of the water source or well. A shallow well is one where the water is within 25 feet of the ground surface. A deep well is where the static water level is more than 25 feet down.
The standing water level in a well is called the static level. This is the water level when the pump is not operating. When the pump comes on and is running there is often a change in the water level. This is referred to as drawdown. The drawdown occurs and the water level reaches what is referred to as the pumping level. This is the operating level of the pump. The lowest level to which the water will drop is the level from which it must be pumped.
Is any source of water where the water is within 25 feet of ground level. When water is pumped from a well the water level will draw down. The lowest level to which it will drop is the level from which it must be pumped.
Types of Pumps – Jet Systems
The first question with jet pumps is what is the suction chamber and how is the vacuum created? The jet assembly itself forms the suction chamber and the vacuum is created by the very high velocity of a stream of water passing through the jet. Basically, the jet assembly is composed of two parts. First, a nozzle which produces the high-velocity stream of water. This high-velocity stream of water is injected through a small compartment which is the suction chamber, thereby causing the vacuum. Obviously, the suction pipe is connected to this compartment or suction chamber. The vacuum caused by the jet permits the greater pressure of the atmosphere on the surface of a body of water to force water into the suction chamber.
The second basic part of the jet assembly is the venturi tube. It is installed in the discharge of the suction chamber. Its function is to convert the velocity of the water into pressure. This is accomplished by the shape of its water passage. Perhaps you can best visualize this by thinking of a nozzle in reverse. The nozzle speeds up the flow of the drive water converting pressure into velocity and when it has passed through the suction chamber, the venturi slows it down again, converting the velocity back into pressure.
“Drive water” is that water which is piped under pressure to the jet assembly or suction chamber. The discharge from the suction chamber or jet assembly is composed of both the drive water and that water pumped from the well. The total amount pumped from the well can be used as discharge from the system and is the output or capacity.
Shallow Well Jet Pump
From the foregoing discussion it is obvious that the operation of the jet system is dependent on the combined functions of both the jet assembly or suction chamber and the centrifugal pump. Also, that these two main components of the system are entirely separate and their locations with respect to each other is a matter of design. In shallow well jet pumps the jet assembly is built into the pump casing, as in the Goulds Pumps J5S. Alternatively, the jet assembly, shallow well adapters, can be bolted to the centrifugal pump. In either case there is only one pipe extending into the well─the suction pipe.
Deep Well Jet Pump
The only basic or fundamental difference between shallow well and deep well jet pumps is the location of the jet assembly. It must always be located in such a position that the total suction lift between it and the pumping level of the water to be pumped does not exceed that which can be overcome by the pressure of the atmosphere. This, of course, means that when this pumping level is at a distance lower than the ground level which cannot be overcome by atmospheric pressure, the jet assembly must be located at least five feet below the low water in the well.
We must have a closed compartment in which to install the nozzle and the venturi and to form the suction chamber. This part is called the jet body. Its shape is such that it will fit into the casing of a drilled well and the pipe connections are located for accessibility. There are two on the top side, one for connection to the pressure pipe which supplies the drive water, the other for connection to the suction pipe which returns both the drive water and the water pumped from the well. For this reason, this connection is one pipe size larger than the pressure pipe. Water from the well enters through a third opening which is on the bottom side of the jet body.
The last accessory for the jet system is the pressure control valve. It is a valve installed in the discharge piping from the centrifugal pump between the pump and the tank, in the pump when the pump is mounted on a tank. Used only in deep well systems, its purpose is to assure a minimum operating pressure for the jet.