Thrush PC2G - Manual (Page 3)

SUCTION PIPING
Long radius elbows should be used in place of standard elbows wherever possible, because of
their superior flow characteristics. Elbows should not be used at suction nozzle, but if it is
unavoidable, long radius elbows should be used. Elbows installed in any position at the suction
nozzle have a tendency to distribute the liquid unevenly in the impeller eye and may cause a
reduction in capacity, create an undesirable thrust condition, or create noisy operation. Eccentric
reducers should be installed directly at the suction nozzle, with the taper at the bottom to prevent
air pockets from forming. Straight taper reducers should never be used in a horizontal suction
line because of the air pocket that is formed at the leg of the reducer and the pipe.
DISCHARGE PIPING
The discharge pipe diameter should be the same as, or larger than, the discharge nozzle
diameter. The size of the discharge pipe to be used is dependent upon its application,
Long radius elbows should be used in the discharge piping as well as in the suction piping to
prevent excessive head loss due to friction. Whenever possible, elbows should be installed
directly at the discharge nozzle as the turbulence created by the elbow will affect pressure gauge
readings.
An increaser should be installed at the discharge nozzle if larger diameter discharge piping is
used. Straight taper increasers and/or reducers are satisfactory in discharge applications.
CAUTION: PROPER PIPING ALIGNMENT IS ESSENTIAL BEFORE CONNECTION IS MADE,
PIPING ALIGNMENT SHOULD NEVER BE ACHIEVED BY FORCE, THIS COULD PRODUCE
STRAIN ON THE PIPING AND THE PUMP CASING. PROPER SUPPORTS SHOULD BE
INSTALLED FOR THE PIPING TO KEEP ITS WEIGHT OFF THE PUMP CASING.
OPERATION
CAUTION: CENTRIFUGAL PUMPS SHOULD NEVER BE STARTED OR RUN DRY.
OPERATING A PUMP DRY WILL CAUSE SCORING OF THE MECHANICAL SEAL,
RESULTING IN PREMATURE SEAL FAILURE. TO PREVENT THE PUMP FROM BEING RUN
DRY, IT SHOULD BE PRIMED BEFORE STARTING.
PRIMING THE PUMP
The pump will not operate satisfactorily until it is primed. All air must be expelled from the suction
piping and pump casing and replaced by the liquid to be pumped. There are several methods of
priming pumps. The one selected will depend on the specific requirements.
FLOODED SUCTION PRIMING
This method of priming a pump is relatively simple – see Figure 2. The liquid source is located
above the pump and all that is necessary to prime the pump is to open the air vent valve or plug
on the pump casing and to crack the gate valve in the suction line. The suction line and pump
should be filled slowly until a steady stream of liquid is observed flowing from the air vent. After
the pump is operating, it is recommended that the air vent valve or plug be opened again to
insure that all air has been expelled from the pump casing.
SUCTION LIFT
A foot valve should be used for priming on suction lift applications, Figure 2. The foot valve
located at the bottom end or foot of the suction piping functions as a check valve, which allows
flow in one direction only, toward the pump. Otherwise, all the liquid may drain from the pump
and suction piping back into the sump after shutdown.
Initial priming is accomplished by completely filling the suction piping and pump casing with the
liquid to be pumped. This can be done by removing the air vent valve or plug at the top of the
pump casing and inserting a pipe nipple in the orifice with an appropriate increaser to
accommodate a hose connection. A priming line can also be inserted in the discharge piping