Primers used to exhaust air from the suction and the casing. Various types of the primers are discussed here. devices. After the pump is primed the at morphemic pressures able to force the water to reach the pump entry.
Various types of the primers are:-
These are reciprocating pumps which develop higher-pressure by the direct action of plunger on the fluid (liquid or gas) confined in a cylinder and forcing the fluid out from the discharge.
Working of Reciprocating Primers:
The piston is driven from the main pump drive shaft by its engagement with the help of a crank shaft & a lever. The priming pump inlet is connected to the delivery side of the main pump h a priming value (air value). The priming value is normally kept closed by means of spring. thus isolating the priming pump from the main pump. During down stroke the air moves above the piston though the value in the piston. Again in the up stroke; the air above the piston is forced out though the outlet drain pipe. By the up & down movement of the piston in the cylinder entire amount of air Is first pushed out, followed by water.
Exhaust Gas Ejector Primers:
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 throw at into a chamber of large dia meter a negative pressures created around the throat.
Construction of Primers:
The essential parts of a jet pump are
The purpose of nozzle is to convert pressure energy to. Velocity energy. The purpose of diffuser, a mixing chamber of motive gases and the entrained fluid, is’ to convert the’ velocity energy back to pressure energy- Jet pumps have no moving parts and thus practice all no maintenance is required.
But they do need high pressure motive fluid which is usually expensive to supply.
Working of Gas Ejector Primers:
When the pump is to be primed the priming value is opened and the exhaust valve closed. The purpose of closing the exhaust ve is to divert the exhaust gases from their normal passage r the exhaust pipe to the silencer. And conduct them to the nozzle of the jet pump which is connected to the casing of the pump.
Rotary Primers (Water Ring Primer):
A water ring primer may be automatic in action boing driven directly room the main pump shaft. This is the primer widely use in the fire service as this can be arranged either automatic or hand operated.
The rotating parts move in relation to the casing so as to create a space which first enlarges drawing in the fluid in the suction line is sealed and then reduces in volume, forcing the automatic or hand operated. through the discharge ports at a higher pressure.
Mounted on the casing of the main pump it is constructed with the following parts.
A rotor or impeller with radial vanes. This has two suction and two discharge ports
Oval shaped casing.
Stationary boss having two suction and two discharge ports.
A waste pipe connected with discharge pipes of two outlet ports.
As the rotor revolves, a small quantity of water which is kept in the casing is thrown by centrifugal force thus leaving a vacuum between the boss of the rotor and the water. When the inlet ports in the casing and those in the rotor coincide, air is drawn in by the vacuum and carried around until the outlet ports are reached. Here as the casing narrows, the fluid is forced out. Thus driving out the air through these outlet ports.
The inlet and outlet ports being duplicated, extremely rapid. And effective priming is achieved. Since the impeller is located centrally in the oval shaped casing there are two pumping actions in one revolution?
Advantages of Rotary Primers:
It has large exhausting capacity.
It gives extremely large rapid and effective priming.
This is suitable for low water levels.
No skills is required in operating.
Pump does not prime
1. Air leak in the primer pump or hose.
2. Delivery valve open.
3. Defective Primer.
1. Check all joints for leaks.
2. Close delivery valve.
3. Examine and rectify.
Failure after disengaging
1. Air leak in pump or suction hose.
2. Air leak through gland packing: or
Mechanical seal of the pump.
1. Check all joints.
2. Adjust ‘gland’ packing repairer
replace mechanical seal.
Chocked suction strainer.
Clean the suction strainer
Broken or crackling jet
1. Suction hose insufficiently submerged.
2. Small leak on suction side of pump.
1. Submerge until vortex disappears.
2. Check pump joints for leaks and rectify.
ADVANTAGES/DISADVANTAGES OF VARIOUS TYPES OF PRIMERS:
A vertical pipe installed in a building for fire fighting purposes, fitted with inlet connections at fire brigade access level and landing valves at specified points, which is normally dry but is capable of being charged with water usually by pumping from Fire Service appliances or form other pressurized sources.
Risers shall be installed in buildings where any floor is at a height of more than (18) meters above ground level.
For building where the upper floor is less than (30) meters above ground level, dry risers can be provided.
For buildings where the upper floor is more than (30) meters above ground level w risers shall be provided.
The Fire Prevention Officer should be consulted in each case.
Each rising main shall be provided with landing valves (hydrant outlets) at various floos levels sited:
Within a ventilated lobby or a lobby approach, where this is provided.
In a stairway enclosure.
In such other positions as may be agreed upon with the Fire Authority.
On selection of positions for inlet connections for a dry rising main, attention shall be paid to the position of fire hydrants available near the building, the possibility of damage resulting from falling parts from windows and other possible occurrences during a fire.
Inlet connections for dry rising main should be installed in an external wall or in a boundary wall of the buildings as close as possible to the position of the main which they serve, and any rim between the inlet and the vertical rim of the main should be given fall towards the drain valve. Easy access shall be provided for the fire brigade to the inlets,
The number and positions of rising mains normally should be such that:
one is provided for each (900) m2
Rising mains are not more than (50) meters apart in horizontal direction.
No part of the floor area is more than (60) meters distant from a landing valve. The distance is to be measured along a route suitable for hose lines, including any distance up or down a stairway.
Dry and wet risers shall be designed in accordance with the approved standards.
The riser should be of galvanized wrought steel piping, heavy quality to BS (1387/1967), screwed and socketed. The fittings to be malleable iron or wrought iron, galvanized and of steam quality.