Piping - Johnson Pump TG GS2-25 Instruction Manual

3.18.6.2 Piping

• Use piping with an equal diameter than the connection ports of the pump and shortest possible.
• The pipe diameter has to be calculated in function of the liquid parameters and the installation
parameters. If necessary use larger diameters to limit pressure losses.
• If the fluid to be pumped is viscous, pressure losses in the suction and discharge lines may
increase considerably. Other piping components like valves, elbows, strainers, filters and foot
valve also cause pressure losses.
• Diameters, length of piping and other components should be selected in such a way that the
pump will operate without causing mechanical damage to the pump/pump unit, taking into
account the minimum required inlet pressure, the maximum allowable working pressure and the
installed motor power and torque.
• Check the tightness of the pipes after connection.
Suction piping
• Liquids should preferably enter the pump from a level higher than the pump level. In case the
liquid should be sucked from a level lower than the pump level, the inclining suction pipe should
rise upwards towards the pump without any air pockets.
• A too small diameter or a too long suction pipe, a too small or blocked strainer will increase
pressure losses so that the NPSHa (NPSH available) becomes smaller than the NPSH
(NPSH required).
Cavitation will occur, causing noise and vibrations. Mechanical damage to pump and pump unit
is not excluded.
• When a suction strainer or filter is installed pressure losses in the suction line must be checked
constantly. Also check if the inlet pressure at the suction flange of the pump is still sufficiently
high.
• When the pump works in both directions, pressure losses must be calculated for both directions.
Self-priming operation
At the start sufficient liquid must be available in the pump filling up the internal clearance volume and
the dead spaces, allowing the pump to build up a pressure difference.
Therefore, for pumping low viscosity fluids, a foot valve with the same or larger diameter than the
suction pipe must be installed or the pump can be installed without foot-valve but in U-line.
Note! A foot valve is not recommended when pumping high viscous liquids.
• To remove air and gases from suction line and pump, counter pressure at the discharge side
must be reduced. In case of self-priming operation, start-up of the pump should be performed
with open and empty discharge line allowing air or gases to escape at low backpressure.
• Another possibility in case of long lines or when a non-return valve is installed in the discharge
line, is to install a by-pass with isolating valve close to the discharge side of the pump. This valve
will be opened in case of priming and allows air or gas evacuation at low backpressure.
The bypass should be lead back to the supply tank – not to the suction port.
32 A.0500.501 – IM-TGGS/05.01 EN (03/2013)