What are Primers? Types of Primers used for exhaust air

What are Primers?

The devices used to exhaust air from the suction and the casing is known as priming devices. After the pump is primed the atmospheric pressure is able to force the water to reach the pump entry.

There are different types of primers which are listed below:

Reciprocating primer:

These are reciprocating pumps which develop higher pressure by the direct action of the plunger on the fluid (liquid or gas) confined in a cylinder and forcing the fluid out from the discharge.


The piston is driven from the drive shaft of the main pump by coupling it with the help of a, crankshaft & amp; a lever. The input of the priming pump is connected to the supply side of the main pump with a priming valve (air valve). The priming valve is normally kept closed by means of a spring, thus isolating the priming pump from the main pump.

During the downward stroke, the air moves above the piston through the valve in the piston. Again in the upward stroke; the air on the piston is expelled through the outlet drain tube. For the top & amp; The downward movement of the piston in the cylinder first expels the amount of air and then the water.

Exhaust gas ejector primer:

These primers find the maximum usage in fire service pumps mounted on vehicles like Fire Tenders.


When a fluid (liquid or gas) under high velocity passes through a throat into a chamber of larger diameter a negative pressure is created around the throat.

The purpose of nozzle is to convert pressure energy to velocity energy. The purpose of the diffuser, a mixing chamber of motive gases and the entrained fluid, is to convert the velocity energy back to pressure energy.


When the pump must be primed, the priming valve opens and the exhaust valve closes. The effect of the closed valve is to divert the exhaust gases from their normal passage through the exhaust pipe to the muffler and to lead them to a nozzle.

The gas is discharged from this nozzle to the throat and, according to the principle of the jet pump, draws the air from the suction and the pump casing through the valve.

Rotary primer:

A water ring primer can be self-acting driven directly from the main pump shaft. This is the primer widely used in the fire service since it can be available automatically or manually.

The rotating parts move in relation to the housing to create a space that first enlarges, the extraction of the fluid in the suction line is sealed and then reduced in volume, forcing the fluid through the discharge orifices at a pressure highest.


  • As the rotor rotates, a small amount of water that remains in the housing is released by the centrifugal force, leaving a gap between the protrusion of the rotor and the water.

  • When the input ports on the casing and those on the rotor coincide, the air is sucked in by the vacuum and transported to the output ports.

  • Here, when the housing becomes narrow, the fluid is forced out, expelling the air through these outlet ports.

  • The ports of entry and exit are duplicated, extremely fast and effective priming is achieved.

  • Since the impeller is centrally located in the oval housing, there are two pumping actions in one revolution.