Check valve having reserved mechanical closure

A check valve has a pivotal arm for striking a flap against a seal that has a knife edge for cutting occasionally lodged debris. The flap without an integral arm is light to provide minimum resistance to flow of fluid in a normal direction. Greater efficiency permits a spring for biasing an actuating mechanism that is aligned with the pivotal arm to be weaker so that fluid can flow more readily in a normal direction and the spring can be reset easier.

BACKGROUND OF THE INVENTION 
This invention pertains to check valves such as used in sewers and in pipes 
conveying liquids in manufacturing plants. More particularly, the present 
check valve relates to mechanical structures for aiding the closing of 
check valves when closure by force of backup liquid fails to provide tight 
closure. 
The present check valve has mechanical closing structure that provides even 
more reliable service than that provided by the valve described in the U. 
S. Pat. No. 4,637,425 issued to the present inventor on Jan. 20, 1987. In 
addition, the material and the pivot of the flap has been changed to 
increase reliability while decreasing the cost of manufacture. 
SUMMARY OF THE INVENTION 
An inlet of the valve for fluid flowing in the desired direction is similar 
to that shown and described in the patent mentioned above. For sealing the 
inlet, a flap usually is pressed by backup fluid against a circular knife 
edge. When tough, pliable material lodges between the flap and the seal, 
an impact against the flap is required for enabling the contiguous knife 
edge of the seal to cut and to dislodge the material. 
In the former valve, an actuating member is biased by a spring such that 
when a catch is released, the member strikes a lever that is solidly 
connected to the flap. Since the impact is sufficient to enable the knife 
edge to cut through almost any debris that is encountered in usual pipes, 
a tight seal is obtained. Although the flap and integral arm as used in 
the valve described in the patent mentioned above are usually light enough 
to permit the flap to be opened far enough by flow in the normal direction 
to prevent debris from collecting in the housing of the valve, 
occasionally, generally after long satisfactory use, debris may collect. 
Also in the former valve, in order that sufficient force is provided for 
cutting through fibrous material, the spring for the actuating member is 
too strong to be reset manually by an elderly person. 
In the present valve, the arm that is struck by the actuating member for 
applying an impact to the flap is pivoted such that the arm can be rotated 
independently of the positioning of the flap. A torsional spring normally 
positions the arm away from the flap so that the flap can be more easily 
opened by normal flow. The use of light plastic, such as 3/32-inch 
(4.0-mm) thick polycarbonate, for the flap, also decreases the force 
required for opening. 
The pivotal arm of the present valve is a separate striking arm that is 
struck by the actuating member, and the momentum of both the actuating arm 
and the striking arm is applied from the actuating member through the 
striking arm as it strikes the flap. Since the present flap without the 
integral arm is light and the striking arm increases momentum for ensuring 
complete closure of the flap, the spring for biasing the actuating member 
can be weaker and still provide the required cutting force.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A usual cast housing 11 of the check valve of FIG. 1 has an inlet 12 and an 
opposite outlet 13. The housing 11 has above the space for usual fluid 
flow, an upper portion 14 to which is bolted a cover 15. A tubular portion 
16 of the cover 15 extends upward from the cover 15 on a vertical line 
that is short distance from the inlet 12 and centered laterally with 
respect to the housing 11 so as to be over a point that is in alignment 
with of the axis of the inlet 12. The tubular portion 16 has sufficient 
inside diameter to receive a rigid actuating member 17, such as a round 
rod, and a coil spring 18 positioned coaxially about the rod. When the 
actuating member 17 is unlatched from an upward position, the spring 
forces the member downward in the housing on a path toward the point in 
alignment with the axis of the inlet 12. 
As described in U.S. Pat. No. 4,637,425, a seat for the inlet 12 comprises 
a cylinder with a knife edge 19 to be contacted by a flap 20. In the 
present valve, the actuating member 17 is aligned with an upper portion of 
a pivoted striking arm 21. The actuating member 17 in response to being 
unlatched strikes the arm 21 and follows it until the arm strikes the flap 
20 such that the momentum of the actuating member 17 and the striking arm 
21 reinforce for providing a substantial impact to the closed or almost 
closed flap 20. 
For positioning a pivotal shaft 23 of both the flap 20 and the striking arm 
21 a short distance from the flap 20 and in line with the vertical 
diameter of the flap 20 as viewed in a closed position, a pair of 
supporting members 22a-b (FIGS. 1 and 3) depend from the cover 15 for the 
required distance to receive horizontally through their lower ends the 
pivotal shaft 23. The lower end of each of the parallel supporting members 
22a-b has a hole on a horizontal line that is substantially in the plane 
of the flap 20, for receiving tightly the pivotal shaft 23. 
With reference to FIG. 3, the pivotal shaft 23 extends through one of the 
two forked arms 24a-b of a metal extension 25 secured to the flap 20, a 
bearing portion 26 of the striking arm 21, and the other forked arm of the 
flap 20. The supporting members 22a-b (FIGS. 1 and 3) are spaced apart the 
required distance to permit the flap 20 and the striking arm 21 to turn 
freely on the shaft 23 while accommodating a turn of a torsional spring 
27, the spring rotating the striking arm 21 away from the closed position 
of the flap 20 while the actuating member 17 is withdrawn. The end of the 
torsional spring 27 extending the farthest from the pivotal shaft 23 is 
shaped to be hooked under the midsection of the striking arm 21, and the 
shorter end of the torsional spring 27 hooks about the adjacent pivot 
support 22a for positioning the striking arm in a slanted position as 
shown in FIG. 1 while the actuating arm member is withdrawn. 
Had the former bearing portions 24a-b of the flap 20 having precise round 
bearing surfaces been retained, the machining during manufacture would 
have to be very accurate to insure a seal between the flap 20 and the 
knife edge 19. Since the closing force either from the backup flow or from 
the striking arm 21 tends to be centrally applied for pressing the flap 20 
tightly against the knife edge 19, the bearing surface through the bearing 
portion 24a-b may be elongated in a direction perpendicular to the surface 
of the flap 20 for permitting precise closure of the check valve without 
requiring precise, expensive machining. Obviously, the semicircular ends 
of the bearing surfaces retain the diameter required for the shaft 23, and 
the intermediate portions are parallel. 
Normally, the actuating member 17 is latched in an upper position, and the 
torsional spring 27 positions the striking arm 21 in the slanting position 
as shown in FIG. 1. Then flow of liquid in the normal direction can easily 
open the light flap 20 as much as required toward the position shown in 
the broken lines in FIG. 1 for permitting full flow of liquid. In response 
to backup flow having entered the housing 15, the flap 20 will be in a 
closed position as shown in full lines. When required, the actuating 
member 17 is released to permit the spring 18 to drive the member 17 
downward for striking the upper portion of the striking arm at a position 
spaced from the pivotal shaft 23. The striking arm has a slightly obtuse, 
intermediate bend in the edge encountered by the lower end of the 
actuating member so that the actuating member 17 strikes rather squarely 
on the upper portion of the striking arm. The impact drives the lower end 
of the striking arm 17 in contact with central portion of the flap 20 that 
is in a closed or nearly closed position as shown in FIG. 2. Any debris 
between the flap and the knife edge 19 is therefore almost certain to be 
cut through, and sufficient space is below the knife edge 19 to permit the 
cut portions to clear the seal. Providing no substantial backup flow is 
present and substantial pressure is provided by fluid that is to flow in 
the normal direction, the tension of the spring 18 as opposed by the 
opposite force of the torsional spring 27 is not sufficient to prevent the 
substantial normal flow. After undesirable back flow is no longer present, 
the actuating member is secured in its upper position to permit fluid to 
flow readily in the normal direction.