14. Operation of vacuum pump
Fire pump cannot pump up water by itself. This is reason why a vacuum pump is used to pump up water to fire pumps.
Vacuum pump is generally of an eccentric rotary type using four blades. Since rotors are installed eccentric relative to main body, four chambers, configured by inside wall of pump body and rotor and blades, are successively changes, in capacity when rotor turns, thus intaking air through suction port, and discharging it through discharge port.
In order to ensure high vacuum performance, it is important to make lubrication, which prevents wear of blades, and forms oil film for air tightness.
The required performance of vacuum pump is such that, when using a suction pipe, 5 m long x inside diameter similar to suction port, vacuum level at closed end of above suction pipe must reach 84% atmospheric within 30 seconds. (No. 35 Ordinance of the Ministry of Home Affairs).
15. Water suction and water discharge precautions
||Attach basket and strainer on suction hose for prevention of entry of sand or foreign matter.
||To prevent sucking air, place suction hose end 30 cm below surface of water.
||Place pump as close to water suction level as possible.
||Be sure to clean machine with fresh water after using muddy water or seawater.
||Connect suction hose tightly using packing.
||Be sure to check and replenish oil to vacuum pump when necessary.
||Never increase speed of vacuum pump unnecessarily.
||In case of water-cooled engine, be sure to complete water suction within about 30 second after starting engine.
||Be sure to always monitor vacuum pump and pressure gauge.
||Determine pressure of pump depending on number of hoses, nozzle bore, nozzle spout pressure, position of nozzle spouts, etc.
||In case of water discharge from pump connected to fire hydrant or other pump, pay due attention as described herein.
||Observe precautions in cold weather as described herein.
16. Suction head (Height)
1) Suction head varies according to the suction tube used and flow rate.
2) Suction head varies with water temperature.
3) Maximum suction head is reduced at the rate of about 0.1 m per 100 m above sea level.
4) Relationship between vacuum level and theoretical suction head is as follows: