It is especially important that suction piping, on
pumps that operate at a high suction lift, be
absolutely free from leaks. If air is drawn in the
suction line through any leaks, the pump
capacity will be reduced and serious difficulties
in maintaining prime may result. When the
suction line draws liquid from an open sump, its
lower end should be submerged sufficiently in
such a way that air is not drawn into the line by
vortex action. A flared suction bell placed on the
end of a vertical suction line will help to
compensate for lack of submergence. A square
steel plate attached to the suction pipe, or a
square floating collar around the vertical pipe,
will also help to suppress vortex action.
Verify that the installation has adequate net
positive suction head available (NPSHa) by
comparing it to the net positive suction head
required (NPSHr) of the pump. Estimating the
NPSHa by merely considering the standing
water level is inadequate since friction losses
through the piping and fittings are generally
significant and must be incorporated into the
NPSHa calculation. Short, simple and large
diameter suction piping with few fittings reduces
suction pressure losses and aids in delivering
adequate NPSHa to the pump.
Discharge Piping
Although discharge piping is not as critical as
suction piping, care should be exercised in
sizing and laying pipe in order to avoid
unnecessary frictional losses. As in suction
piping, the number of fittings should be
minimized and abrupt changes in direction and
size of piping should be avoided.
A gate valve should be installed in the discharge
line; it will be of assistance when priming the
pump and will permit service to be performed on
the pump without needing to drain the discharge
line and any connected vessels. It is advisable
to install a check valve in the discharge line
between the pump and gate valve in a system
operating at high discharge heads and with a
foot valve on the suction line. The check valve
protects the pump from pressure surges which
occur when the pump is stopped. In pressure
systems without a foot valve, the check valve
prevents reverse rotation of the pump and loss
of pressure in the discharge line if the pump
stops. For systems with very high discharge
heads (above 80 psi), a non-slam check valve
should be used.
Foundation and Installation
Close-coupled pumps are assembled into a rigid
unit which requires a minimum amount of
preparation for mounting. Nevertheless, this type
of pump should be bolted down securely,
otherwise it is possible to shift position during
operation which could impose high stresses to
the unit and cause premature failure.
There are two primary ways to mount the pump:
bolting the pump assembly straight onto a
foundation (such as concrete), or installing a
baseplate onto the foundation and installing the
pump assembly onto the baseplate.
The general requirements of the foundation are:
•The foundation must be a rigid support for
the unit and be able to absorb loads
imposed on the unit and any type of
vibration
•It is absolutely necessary to provide a flat,
horizontal mounting surface. A flat
foundation is required to prevent strain and
distortion when tightening the foundation
bolts.
•The foundation must weigh at least 2-1/2
times the weight of the pump unit
In the case of installing the pump onto a
foundation (such as concrete):
•In order to be able to take advantage of the
back pull-out design of the Griswold 850
Series pumps, it is recommended to install
some type of female threaded inserts into
the foundation for hold-down bolting. This
will allow the user to remove the hold-down
bolts and pull the pump back away from the
casing, which may not be feasible if the unit
is bolted down to the foundation through
studs which are bonded into the foundation.
In the case of installing the pump with a
baseplate:
•A sleeve type anchor bolt can be utilized,
whereby the anchor bolts are inserted in
pipes or sleeves having a diameter of 2 or 2
