Metal working – Method of mechanical manufacture – Gas and water specific plumbing component making
Reexamination Certificate
2000-06-23
2001-09-25
Larson, Lowell A. (Department: 3725)
Metal working
Method of mechanical manufacture
Gas and water specific plumbing component making
C072S370040
Reexamination Certificate
active
06293013
ABSTRACT:
BACKGROUND
This invention relates to a backflow preventer.
Backflow preventers are principally to prevent contamination of a public water distribution system by reducing or eliminating backflow or back-siphonage of contaminated water into the system. Usually, the backflow prevention assembly is installed in a pipeline between a main supply line and a service line that feeds an installation, e.g., a hotel, factory or other institution, or even a multiple or single family residence. A backflow prevention assembly typically includes two check valves that are configured to permit fluid flow only in the direction from the main supply line to the service line.
FIG. 1
illustrates a conventional connection between a valve module
40
′ and a housing
20
′ of a prior art backflow preventer. As shown, an annular mount
90
having an threaded inner surface
92
and a smooth outer surface
94
is secured to a cylindrical inner surface
96
of housing
20
′, e.g., by solder
98
or welding
99
. The valve module
40
′ is then screwed into mount
90
to secure it to the housing.
SUMMARY
In one aspect, the invention is directed to a backflow prevention assembly. The backflow prevention assembly has a unitary housing with a passage therethrough, two threaded regions formed in an inner surface of the unitary housing, and two valve assemblies positioned in the passage to prevent fluid flow in a direction. Each valve assembly has an annular mount having a threaded outer surface that engages one of the threaded regions on the inner surface of the housing.
Implementations of the invention may include the following features. The two valve assemblies may be cam-check valves. The threaded regions may be formed by a thread rolling process, e.g., by placing a threaded die against the inner surface of the housing and pressing on an outer surface of the housing. Threaded regions may also be formed in the outer surface of the unitary housing.
In another aspect, the invention is directed to a method of forming threads in a tubular housing. In the method, a die having a thread on an outer surface thereof is placed in contact with an inner surface of a unitary housing having a passage therethrough. The outside of the housing is pressed to drive the inner surface against the threads on the outer surface of the die to form threads on the inner surface of the housing.
Implementations of the invention may include the following features. The thread on the outer surface of the first die may be generally the inverted shape of the threads to be formed on the inner surface of the housing. A second die having a thread formed on an outer surface thereon may be use to press on the outside of the housing. Two valve assemblies may be positioned in the passage to prevent fluid flow in a direction, each valve assembly having an annular mount having a threaded outer surface that engages one of the threaded regions on the inner surface of the housing. A port may be formed in a wall of the housing.
Advantages of the invention may include the following. The backflow prevention assembly is easier to assemble, e.g., in the field, and is less expensive to manufacture than currently available backflow prevention assemblies for similar applications.
Other features and advantages of the invention will become apparent from the following detailed description, including the drawings and the claims.
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“Series 994/994RPDA” ©1997, Watts Regulator, Watts Industries, Inc., Water Products Division—Safety & Control Valves, North Andover, MA.
“Series 774/774DCDA, 774X/774XDCDA” ©1998, Watts Regulator, Watts Industries, Inc., Water Products Division—Safety & Control Valves, North Andover, MA.
PCT International Search Report fot International Application No. PCT/US 00/32718.
Fish & Richardson P.C.
Larson Lowell A.
Watts Investment Company
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