Volume 8 – Mechanical and Electrical Services - Malaysia Geoportal

Chapter 1 PUMPING INSTALLATION
1.9 PIPING, VALVES, JOINTS & SUPPORTS
Normally steel pipes are commonly used for discharge piping system where the medium being
handled is not acidic or corrosive. Ductile iron pipes would be used when handling acidic liquid
because of its high corrosive resistible characteristics. When steel pipes are used, they are either
galvanized or coated with coal tar enamel. Sometimes, high-density polyethylene (HDPE) pipes are
used in place of steel pipes because of its excellent chemical and corrosion resistant properties.
They are much lighter per meter length, tough and durable. Because of the exceptional smooth
inner surface, friction loss in water flow is minimized.
Determination of pipe wall thickness shall be based on the tensile stresses due to internal pressure
and stresses produced by the bending of the pipe due to external pressure when buried
underground. Where long pipeline is installed, due consideration shall be given to impact pressure
due to water hammer. An allowance of 1 ~ 2mm thickness is allowed for against corrosion.
Pipes should be adequately supported. Supports should be provided near changes in direction,
elbows, branch lines and near valves. Valves and other heavy piping components should be
individually supported. Long vertical pipes should be fixed not only at the lowest part but also at the
intermediate locations with center rest fittings to aloe for expansion. Pipes laid on slope shall be
fixed in such a manner that sliding in the axial direction is prevented. Concrete thrust blocks must
be provided to resist the force or combination of forces which tends to produce joint separation. A
pipe to which a flexible / expansion joint is installed should be supported properly at locations close
to the joint.
Buried pipes should be properly supported and aligned to avoid settlement. Cover to buried pipes
shall not be less than 900mm from ground surface. The cover shall be increased to 1200mm from
ground surface underneath roadway unless specially protected.
Valves commonly used in DID pumping applications can be classified into three categories as
follows:-
a) valves for flow control
b) valves for stopping water flow
c) valves for reverse flow prevention and
d) valves for surge control.
Gate valves are commonly used in both shutting off and flow control. Where frequent opening and
closing operation is not required, non-rising stem type is preferred. To prevent back flow of water
upon pump stop, flap valves are installed at the end of the discharge pipe or alternatively swing
check valves are provided close to the pump discharge end. Where water hammer effect is
expected, special type of fast-closing check valves or pump control valves might be useful in
controlling surges.
1.10 PUMP SUMP DESIGN AND DIMENSIONS
To ensure reliable and efficient pump performance, it is essential that the hydraulic design of the
intake structure produce satisfactory flow conditions at the inlet to the pump. Pump sump design
covers (a) submergence, (b) floor clearances, (c) sump design and (d) sump intake or flow
distribution in the sump.
March 2009 1-13