M&H 4500, Руководство пользователя

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Page 17 of 27
SECTION 4
OPERATION OF M&H BFVS WITH
TRAVELING NUT OPERATORS
SECTION 4.1 – GENERAL
Operational criteria for rubber seated Butterfly Valves (BFV) is covered is in the Appendix section of
AWWA C504. Briefly stated, some of the important information includes:

Does not permit the operation of any valve at pressures above the rated pressure of the
valve.

Do not exceed 300 ft-lb input torque on operators with wrench nuts and do not exceed
200 lb rim pull for handwheel or chainwheels against the Open or Closed Stops.

If a valve is stuck in some intermediate position between open and closed, check first for
jamming in the operator - and “do not force the vane open or closed” which can severely damage
internal parts.
SECTION 4.2 – INPUT TORQUE
M&H traveling nut operators exceed with the AWWA C504 torque recommendations. They are designed
to OPEN or CLOSE the valve at LESS THAN 150ft-lbs of input torque. M&H traveling nut operators
are also designed to withstand 450ft-lbs of input torque against the STOPS (in the full OPEN or CLOSED
position). Torque in excess of these limits may damage the valve or operator or both. This safety factor
may be less prevalent with third party operators that may or may not be AWWA C504 compliant.
Maintenance personnel should be aware of the type of operators being used before actuating the valves.
SECTION 4.3 – THROTTLING
The M&H traveling nut operator is designed hold in place at any intermediate position and not allowing
line flow to move the vane. Throttling operations that generate velocities up to 16 feet per second (fps)
are acceptable and covered in the AWWA standard for class ‘B’. However, a BFV is not considered a
pressure regulating valve and is not designed for prolonged operation at less than 20 degrees open.
SECTION 4.4 – WATER HAMMER
Water Hammer is a hydraulic shock to a water system from a pressure surge, sudden stoppage or change
in direction. Extreme water hammer effects can severely damage a water system (lines, valves, and other
components). When opening or closing valves, consideration must be given to the potential for water
hammer as a result of opening or closing a valve too rapidly.
An M&H traveling nut operator incorporates the benefit of opening and closing slowly (assuming a
consistent input speed) as the operator reaches the ends of its travel. This serves to minimize the potential
for water hammer effects. Despite the anti-water hammer characteristics, it is still encouraged to establish
operational policies relating to valve closure speed that will reflect all possible hydraulic conditions. This
should include the possibility of high velocity line break conditions. Despite the urgency of a line break,
slow closure is critical to minimize the potential for operational failure of the valve or the piping system
and its restraining systems.