CHAPTER 3PUMPS TEXT1 WORDS AND EXPRESSIONS
TEXT A pump is a machine used to raise liquids from a low point to a high point. A pumping system on a ship consists of suction piping, a pump and discharge piping. Every pump has a power end, which may be a steam turbine or an electric motor and a liquid end where the liquid enters or leaves the pump The typical characteristics for the pump are the suction head and the discharge head The suction head is the pressure of the liquid entering the pump or the difference in the level of liquid with respect to the level of the pump on the suction side. The discharge head is the pressure of the liquid leaving the pump or the level of liquid with respect to the level of the pump on the discharge side. There are three main classes of pumps in marine use: displacement, axial flow and centrifugal.Displacement pumps can be either reciprocating or rotary. The operating principle of the reciprocating displacement pump is the following. As the piston moves upwards suction takes place below the piston and liquid is drawn in, while the discharge valve is closed. Above the piston liquid is discharged and the suction valve is closed. As the piston travels down the operations of suction and discharge occur on opposite sides. A relief valve is always fitted between the pump suction and discharge chambers to protect the pump against excessive pressure. The rotary displacement pumps operate by means of rotary parts which trap the liquid at the suction side and force it through the discharge outlet. According to the type of rotary-elements there are rotary vane displacement pumps.gear displacement pumps and screw displacement pumps. An axial flow pump useas a screw propeller to axially accelerate the liquid.The outlet passages and guide vanes are arranged to convert the velocity increase of the liquid into a pressure. In a centrifugal pump liquid enters the centre of the impeller and flows radially out between the vanes.A diffuser or volute is then used to convert most of the kinetic energy in the liquid into pressure.There are single-entry or double-entry centrifugal pumps. (1700)
TEXT 2 OPERATION AND MAINTENANCE INSTRUCTIONS WORDS AND EXPRESSIONS
TEXT Starting (the centrifugal pump and axial flow pump) 1) Open the suction check valve wide, opening at the same time the air vent on the top side. 2) Close the air vent as soon as liquid flows out of it. 3) Start the motor leaving the discharge valve closed. 4) Check that direction of rotation is as indicated by the arrow. 5) Slowly open the discharge check valve until operating requirements are reached. 6) Check on the ammeter that power requirements do not exceed the motor possible rating. 7) Check tightness of the packing gland. Leaks must be reduced to a few drops which is required to prevent harmful heating of the packings and the shaft.
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