15 August 2002
Pump suction chamber,
Pump suction bells,
Discharge check and gate valves,
Discharge culvert including backwash trash rack, and
Hinged stop gate, sliding stoplog or discharge sluice gate.
Where pumping plants may be designed to remove water from more than
one dock, additional suction sluice gates are required to permit independent pumping of
Make available an emergency drainage pump, which may be a
submersible type, in the event of an emergency or when a drydock must be isolated
Elevation of Discharge. The most desirable operational pumping
arrangement (especially where tidal range is not great) is a system in which the
discharge is directly overboard above high tide, and in which no discharge check and
gate valves, trash racks, or stop gates are required. Operation is simplified as there is
no large power driven valves with electrical controls to be operated and maintained.
Design. The design outlined above allows elimination of a large portion of
the pumproom substructure, with an accompanying reduction in pumping plant initial
cost. This design is not well adapted to a site where extreme high water rises to within
less than 1.83 m (6 ft) of the coping level. The additional elevation required in delivering
water overboard above high tide increases the total static pumping head. This increase,
however, may be more offset by reduction in friction owing to elimination of the pump
check and discharge valves.
Pumping Head. The pumping head of the main dewatering pumps is the
sum of the maximum hydrostatic head and hydraulic system losses. See Figure 7-1.
Maximum hydraulic system losses exist when maximum flow occurs, which is the time
of minimum static head.
Pump Suction. With reference to design and satisfactory functioning, the
most critical portion of a hydraulic system is the suction portion extending from dock
chamber to dewatering pump suction bell. This portion consists of the suction inlet,
suction pit below the inlet, and conduits leading from the pit to individual pumps or to a
pump suction chamber common to all pumps, and the pump suction bells. If the
conduits are separate for each pump suction, sluice gates may be installed in each
conduit to permit working on a pump without impairing the use of other pumps.