Valve and Gate Operators.
1. Threaded Stem Hoist.
Basically a threaded stem type hoist consists of a steel, Acme-threaded stem
mated to a bronze stem nut. Depending on the application, the stem or the stem nut may be rigidly attached
to the gate. In a rising stem type gate, the nut is rotated, and the stem rises with the gate. In some cases,
the stem is rotated, and the gate rises with the stem nut. In most cases, the hoist is electric motor driven
through a system of gears. Ring-seal gates and some jet-flow gates use threaded stem type hoists with twin
stems. Threaded stem hoists are shown in
2. Chain and Sprocket Hoist.
Chain and sprocket hoists are used to raise or lower large gates which are
used infrequently. The hoists are powered by an electric motor which drives a reduction unit with two
output shafts. The output shafts each drive a hoist unit with reduction gearing, drive sprocket, idler
sprocket, and sprocket chain. One end of each chain is attached to the gate and the other to a counter
weight. A typical chain and sprocket hoist is illustrated in
3. Wire Rope Hoist.
Wire rope hoists are most commonly used with radial gates. Wire rope hoists
4. Hydraulic Operators.
Hydraulic operators are used for a variety of gates and valves. Basically a
hydraulic system consists of an oil reservoir, electric motor driven pump, directional, relief, check, flow
control, and shutoff valves, filters, and the operator itself, usually a hydraulic cylinder. Many systems use
two pumps in parallel to provide a backup should one fail. The operator may be driven in both directions,
or it may be powered open and allowed to close by gravity. Examples of hydraulic systems are shown in
3.3 Guard Gate and Valve Closure Tests
Closure tests of all outlet works and power penstock guard gates and valves are required periodically to
verify gate and valve dependability and determine maintenance requirements. While some gates and valves
can only be tested under balanced conditions, most should be given a simulated emergency closure test
under maximum flow, full load conditions.
The purpose of these tests is to ensure that the gates/valves will operate as intended under severe, but
controlled, conditions. If the gate/valve fails to operate as intended during these tests, the regulating
gate/valve or the wicket gates are still available to stop the flow. In an actual emergency situation, such as
failure of regulating gate/valve, a ruptured penstock, multiple shear pin breakage, or loss of governor
control, the guard gate/valve would be the only means of stopping flow.
The gates/valves requiring simulated emergency closure tests are designed to close under full flow
conditions with no damage, but it is essential that the correct test procedure be followed exactly. If there is
any doubt about the validity of the test procedure or if a written procedure for a particular gate or valve is
not available, contact the Hydroelectric Research and Technical Services Group, D-8450, immediately.
The emergency closure tests should be scheduled to fit into the regular maintenance schedule. The tests
many times can be set up to correspond with preventive maintenance on the gate, with the gate taken out of