What is a diaphragm pump?
A diaphragm pump is a type of a type of positive displacement pump that uses the reciprocating action of a flexing diaphragm to move fluid into and out of the pumping chamber.
They work when the flexing diaphragm creates a vacuum at the inlet of the chamber that draws the fluid into the chamber. When the diaphragm moves in the opposite direction, it causes the volume of the pumping chamber to decrease, forcing the fluid out the discharge port of the pump.
Diaphragm pumps use check valves at the inlet and outlet of the pumping chamber to ensure that the fluid flows in one direction and out the other without leaking backwards.
They generally work within the following ranges:
- Flow rate ranges between 1 and 1,800 gpm
- Total head (pressure) ranges between 25 and 15,000 psi
- Horsepower ranges between 0.5 and 2,000 hp
How do they work?
There are four main types, with the chief distinction of each being the mechanism that drives the reciprocating diaphragm:
1. Mechanically actuated - have a reciprocating mechanical linkage that is directly attached to the diaphragm. The pump includes a gear set or other mechanical mechanism to convert the rotation of the motor into a reciprocating motion of the linkage that is attached to the diaphragm. Flow may be varied by varying the stroke length or pump speed.
2. Hydraulically actuated - employ an intermediate hydraulic fluid located on the non-product side of the diaphragm to flex the diaphragm. The hydraulic fluid is pressurized by a reciprocating plunger. Though it acts similar to a mechanically actuated diaphragm, the plunger isn’t attached to the diaphragm, but rather pressurizes the intermediate hydraulic fluid, which flexes the diaphragm. Flow is varied with this type of diaphragm pump by varying pump speed or by varying the amount of hydraulic fluid that is bypassed.
3. Solenoid - have an electric motor that alternately energizes and de-energizes a solenoid, which creates an electro-magnetic force that reacts with a metal part on the diaphragm, causing the diaphragm to flex. Flow is varied by varying the pump speed.
4. Air operated double diaphragm pumps (AODD) - a type of double acting pump. They have two diaphragms and two sets of check valves. The pump is driven by compressed air operating alternately on the non-product side of one diaphragm, and then the other. The air is delivered to the alternate sides of the diaphragm by means of a shuttle valve. Flow is varied by varying air pressure supplied to the pump.
Where are they used?
Diaphragm pumps are used in many applications across the commercial, industrial, municipal, and scientific fields. They are commonly used as metering pumps to pump precise volumes of liquid for treating water (e.g., drinking water, waste water, boiler water, swimming pool water, etc). They are used in process applications where very high pressures are required, where metering of fluids is needed, or where the sealless nature of this pump type is an important benefit. And AODD pumps are used to move liquids containing solids or where electricity is not available.
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