Fluid handling – Line condition change responsive valves – Direct response valves
Patent
1997-05-19
1998-05-05
Ferensic, Denise L.
Fluid handling
Line condition change responsive valves
Direct response valves
137527, F16K 2110
Patent
active
057462461
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a water hammer preventing check valve to be placed in a fluid conveying pipe, capable of safely and reliably preventing water hammer in a pipeline caused by a reverse flow of the fluid when a pump is stopped suddenly. In this specification, the term, "water" is used as a general term signifying a fluid, and terms "upstream side", "downstream side", "inlet" and "outlet" are used to designate positions and directions with reference to the normal direction (not the reverse direction) of flow of the fluid.
BACKGROUND ART
If the operation of a check valve placed in a water supply pipe is unable to follow an abrupt change in the flowing velocity of water flowing through the water supply pipe resulting from the stoppage of a pump and if the valve element of the check valve is seated on the valve seat of the same during the reverse flow of water, water hammer is created on the downstream side of the check valve, which, in some cases, causes serious troubles. Inventions relating to check valves having water hammer preventing capability are disclosed in, for example, JP-B No. 40-3654, (Water Hammer Preventing Pumping Apparatus), JP-B No. 51-25930 (Improvements in Water Hammer Preventing Pumping Apparatus) and JP-B No. 63-60274 (Swing Type Water Hammer Preventing Check Valve). These inventions will be referred to as "prior inventions". As is known, those inventions have prevalently been put to practical use. The present invention relates to improvements in the water hammer preventing check valves of the prior inventions.
The water hammer preventing check valves of the prior inventions are based on technical ideas technically superior to conventional technical ideas of preventing water hammer which have been prevalent symptomatic water hammer preventing ideas allowing a valve element to be seated on a valve seat during the reverse flow of a fluid and retarding the movement of the valve element by a braking means to ease shocks, using an automatic valve or a surge tank to relieve and cushion pressure rise resulting from water hammer. It can readily be gathered from descriptions in the specifications of the prior inventions that the technical concepts on which the prior invention are based include radical improvements intended to stop a reverse flow in a pipe for the positive elimination of causes of water hammer by forming a valve element and flow passages around the valve element so that the valve element is about to be seated on a valve seat at a moment when the inertial flow of a fluid in a discharging direction in the pipe stops after the pump has been stopped.
As shown by way of example in FIG. 5, a water hammer preventing check valve of the prior invention is constructed so as to eliminate as many factors obstructing the closing motion of a valve element as possible; that is, a valve element is designed so that the valve element has a reduced mass, the least possible form drag and the least possible inertial resistance. This valve element is capable of appropriate closing motion by its own weight following the reduction of flow velocity without delay, the closing motion of the valve element is corrected by biasing the valve element in the closing direction by a weight or a spring if there is any error in the closing motion of the valve element, and the valve element achieves water hammer prevention almost satisfactorily. However, when putting this water hammer preventing check valve of the prior invention to practical use, the water hammer preventing check valve is still encountered by the following technical problems.
(A) When supplying water into a pressure tank installed near a pump or when one of a plurality of pumps installed close to each other is stopped abruptly while the plurality of pumps are in parallel operation, the potential force of the inertial flow of water column in a pipe downstream of the pump is relatively small because the pipe downstream of the pump is short, whereas the pressure in the pressure tank or the discharge pressures of the adja
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Yokota Hiroshi
Yokota Shingo
Ferensic Denise L.
Kabushiki Kaisha Yokota Seisakusho
Kim Joanne Y.
Yokota Hiroshi
Yokota Shingo
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