Starting of Reciprocating Pumps
Reciprocating pumps are positive displacement pumps that can handle air along with the liquid that is pumped. When started for the first time, the pump will work irregularly for several strokes because the whole pipe system will be full of air. Pumps should therefore be flooded with the liquid they are to handle, which prevents seizure or wear, especially when priming a long suction line.
Reciprocating pumps are normally used in bilge systems in ship's machinery spaces. Bilge system consist of bilge wells (Collecting wells where all drains and leakages in the engine room are collected), bilge pipe lines and bilge pump. Bilge wells are located in engine room tank top (Lowermost part in engine room), while pump is situated in engine room floor, above the tank top. So the pump has to suck the liquid up. Hence most of the ships use reciprocating pumps as bilge pumps.
Procedure to Start an Electric Motor Driven Reciprocating Pump
- Make sure power is on for the electric motor.
- Check for lubrication. Ensure proper level of lubricating oil inside the pump gear box.
- Open pump and line suction, discharge valves. Make sure the line is clearly set. Do not shut the valves and run reciprocating pumps.
- Open the vent cock fitted at the discharge side of the pump. Intermittent discharge from the cock indicates air trapped in the system or pump is not primed.
- Check both suction and discharge pressure gauges for normal readings. Cocks for both pressure gauges must be in open position always. Otherwise it gives a wrong indication, even if pump is working satisfactorily.
Indications of Suction Pressure Gauge
Approx.760 mm Hg vacuum
Blockage in the suction line, due to chocked line filters or pump suction filter which causes vacuum in the system
Air lock in the system, may be due to improper sealing of filter covers, leaking pump gland, leaking valve chest cover, holes in the pipe lines, etc.
Approx.100 - 400 mm Hg vacuum
Pump is operating normally, taking suction from bilge wells
Positive Pressure (Pressure higher than zero, not vacuum)
Suction from a level higher than the pump, possible when seawater priming valve is open
Indications of Discharge Pressure Gauge
1.0 - 3.0 Bar and Steady Reading
Pump is working normally. Only liquid comes out of the air vent cock at the discharge.
Very little or no air in the air vessel
Very High (Maximum of the Scale)
Blockage in the discharge line, possibly closed discharge valve