Note: Descriptions are shown in the official language in which they were submitted.
CA 02330002 2001-01-02
WATER HAMMERING PREVENTION DEVICE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a water hamming prevention
device.
2. Description of the Prior Art
It has been a common practice to use an accumulator
installed in the middle of the piping system of the water supply
device to achieve such an object.
Such a device has a sealed container whose inside is
divided into the water supply pressure side and the pressure
suction side by means of a rubber bladder, diaphragm, piston,
etc., so that the pressure surge due to the water hammering
action generated at the water supply pressure side can be
absorbed.
However, there was a limit to the absorption of the
pressure surge due to the water hammering action because the
pressure absorption side of the abovementioned device is a
closed space.
SUMMARY OF THE INVENTION
With the abovementioned problem in mind, the present
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invention intends to provide a water hammering prevention
device characterized in comprising: an outer box having
concentric flow paths for an inlet and an outlet and a drain
port in the midstream section of the flow path; an inner tube
member having a diaphragm on its periphery dividing the inside
of said outer box into an upstream section and an area consisting
of a midstream section and a downstream section of the flow
path, wherein said inner tube member slidingly fits into the
upper section; a relief valve provided on the end face of the
downstream side opening of said inner tube member, wherein said
relief valve is capable of moving toward or away from a valve
seat located on the periphery of a valve port, which is
provided between the midstream section and the downstream
section, and is energized by a relief valve spring toward the
valve opening direction; and a check valve provided inside the
inner tube member to prevent fluid from flowing backward from
the downstream side, thus solving the abovementioned problem
by discharging the pressurized water caused by the water
hammering action to the outside via the drain port.
An embodiment of the present invention checks the
upstream side with the check valve and opens the
relief valve when the back pressure rises above the
upstream pressure due to water hammering, so that the back
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CA 02330002 2006-09-27
pressure from downstream can be discharged to the outside
through the drain port, thus eliminating noise and vibration
due to water hammering completely and drastically reducing
piping system problems, which used to be caused at least
partially by noise and vibration due to water hammering.
According to another aspect of the invention the
water hammering prevention device is installed parallel
to the check valve installed in the piping of the water
supply device, or directly in the piping, and the drain
port is connected via piping to the water receiving
tank, so that it not only prevents water hammering
completely but also it adds an economic effect of
eliminating wasteful use of water as the water drained
from the drain port is returned to the water receiving
tank. A water hammering prevention device is connected
to each of the terminal devices of the water supply
device and their drain ports are connected to the
outside, so that it is capable of preventing water
hammering caused by frequent high back pressure rises
due to repeated turning on and off of the water
supply, particularly when the terminal devices are
high pressure water injection guns, by discharging
the high pressure fluid to the outside through the
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CA 02330002 2006-09-27
drain port.
By connecting the drain ports via piping to the
water receiving tank, water waste can be prevented
as well.
According to a further aspect of the invention
since the effective diameter of the diaphragm and
the valve seat diameter of the valve seat are
chosen to be about equal so that the valve closing
pressure of the relief valve that the diaphragm
receives and the valve opening pressure that the
relief valve itself receives can be balanced and
the spring loads of the relief valve spring and the
check valve spring respectively are chosen to
maintain the pressure of the midstream section
always lower than the upstream side pressure by a
margin of Z~P of a constant value, it is possible to
provide, by setting the pressure difference LP
between the pressure of the midstream section and
the upstream side pressure to match the individual
characteristic of a water supply device, a
specific valve opening characteristic for the
relief valve to suit the characteristics of a
particular water supply device, thus being able to
provide a water hammering prevention device that
fits with any water supply device.
According to a further aspect of the
invention the inner tube member is formed to
have a circular cross section, while the sliding
surface of the inside of the outer box that fits
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CA 02330002 2006-09-27
with the inner tube member has grooves equally
spaced along its circumference, so that it is
possible to reduce the sliding contact area between
the inner tube member and the sliding surface and to
make the inner tube member thinner and lighter
without sacrificing strength, thus contributing to
reducing the sliding resistance of the inner tube
member as much as the strength of the inner tube
member allows. Consequently, it is possible to
improve the water supply performance because of the
reduction of the pressure loss of the pressurized
fluid during the water supply period and to use a
smaller water supply pump for the water supply
device.
According to a further aspect of the invention
it is possible to reduce the friction resistance of
the inner tube member against the outer box because
of a coating on the outer circumference of the inner
tube member of TeflonTM and to reduce the pressure
loss in the same way as in the case above.
According to a further aspect of the invention
the check valve has a flat surface formed on its
face confronting the check valve port, said
surface having a diameter smaller than the check
valve port, and a conical apex formed in the
middle of said flat surface. Furthermore, multiple
tilting grooves are provided having a groove width
CA 02330002 2006-09-27
decreasing gradually toward the center of the back of
the check valve from the outer periphery, which is
further outside of a seating area corresponding to
the check valve seat. These tilting grooves are
equally spaced in the circumferential direction on
the check valve. As a result, water flows smoothly
from upstream to downstream along the shape of the
check valve without causing any swirls on the back of
the check valve, thus minimizing the pressure loss
due to the check valve inserted in the flow path. It
provides similar effects as mentioned above and its
practical benefit is significant.
According to an aspect of the present invention there
is provided a water hammering prevention device comprising
an outer box having concentric flow paths for an inlet and
an outlet and a drain port in a midstream section of the
flow path, an inner tube member having a diaphragm on its
periphery dividing an inside of the outer box into an
upstream section and an area consisting of the midstream
section and a downstream section of the flow path, wherein
the inner tube member slidingly fits into the upstream
section, a relief valve provided on an end face of a
downstream side opening of the inner tube member, the relief
valve being capable of moving toward or away from a valve
seat located on the periphery of a valve port provided
between the midstream section and the downstream section,
the relief valve being energized by a relief valve spring
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toward a valve opening direction, and a check valve provided
inside the inner tube member to prevent fluid from flowing
backward from the downstream side, wherein an effective
diameter of the diaphragm is chosen to be approximately
equal to a valve seat diameter of the relief valve in order
to achieve a pressure balance between a valve closing
pressure and a valve opening pressure applied to the relief
valve, and spring loads of the relief valve spring and a
check valve spring, which check valve spring energizes the
check valve in a valve closing direction, are chosen so that
a midstream pressure is always lower by a constant value
than an upstream pressure.
According to another aspect of the present invention
there is provided a water hammering prevention device
comprising an outer box having concentric flow paths for an
inlet and an outlet and a drain port in a midstream section
of the flow path, an inner tube member having a diaphragm on
its periphery dividing an inside of the outer box into an
upstream section and an area consisting of the midstream
section and a downstream section of the flow path, wherein
the inner tube member slidingly fits into the upstream
section, a relief valve provided on an end face of a
downstream side opening of the inner tube member, the relief
valve being capable of moving toward or away from a valve
seat located on the periphery of a valve port provided
between the midstream section and the downstream section,
the relief valve being energized by a relief valve spring
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CA 02330002 2004-07-19
toward a valve opening direction, and a check valve provided
inside the inner tube member to prevent fluid from flowing
backward from the downstream side, the check valve having a
flat surface formed on its face confronting a check valve
port, the flat surface having a diameter smaller than the
check valve port, a conical apex formed in the middle of the
flat surface, and multiple grooves formed in an equally
spaced manner in the circumferential direction on the check
valve and having a groove width decreasing gradually from an
outer periphery of the check valve toward a center of a
downstream side thereof, the outer periphery being located
outwardly of a seating area corresponding to a check valve
seat.
According to a further aspect of the present invention
there is provided a device for preventing water hammer
comprising a housing defining a flow path having an inlet
end, an outlet end and a drain port disposed between the
inlet and outlet ends, an inner tubular member slidably
disposed within the housing, and an annular diaphragm
interconnecting a periphery of the tubular member with the
housing and dividing the flow path into an upstream side and
a downstream side, a relief valve including a valve member
defined on a downstream end of the tubular member and a
valve seat provided in the housing, the valve member being
biased in an opening direction away from the valve seat by a
first spring, and a check valve slidably disposed within the
tubular member to prevent a reverse flow of fluid within the
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CA 02330002 2004-07-19
device, the check valve being biased in a closing direction
by a second spring, the diaphragm having an effective
diameter which is substantially equal to a diameter of the
valve seat to provide a balance between valve closing and
opening pressures imposed on the valve member and the loads
of the first and second springs are set such that a
downstream pressure is lower than an upstream pressure to
normally maintain the relief valve in a closed position when
fluid is flowing through the device and also when fluid is
not flowing through the device, and upon the downstream
pressure becoming higher than the upstream pressure due to
water hammer, the relief valve opens to allow discharge of
pressurized fluid into the drain port.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross sectional view showing the water
hammering prevention device when water is not running.
Fig. 2 is a cross sectional view showing the water
hammering prevention device when water is running.
Fig. 3 is a cross sectional view showing the water
hammering prevention device when water hammer occurred and it
is draining water.
Fig. 4 is a drawing showing various dimensions of the
water hammering prevention device.
Fig. 5 is a cross sectional view along A-A of Fig. 1.
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CA 02330002 2001-01-02
Fig. 6 is a plan view showing a modified version of the
check valve.
Fig. 7 is a front view of the check valve shown in Fig.
6.
Fig. 8 is a bottom view of the check valve shown in Fig.
6.
Fig. 9 is a cross sectional view along B-B of Fig. 6.
Fig. 10 is a drawing for showing an example of piping
for a water supply device with the water hammering prevention
device built in.
Fig. 11 is a drawing for showing another example of
piping.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Let us describe a preferred embodiment of the invention
referring to the drawings.
Figs. 1 through 3 show the cross section of the water
hammering prevention device according to the present invention
in various conditions.
Fig. 1 shows the status when water is not running, Fig.
2 shows the status when water is running, and Fig. 3 shows water
being drained as water hammering has occurred.
This water hammering prevention device 1 consists of an
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outer box 2, an inner tube member 3, a relief valve 4 and a
check valve S.
The outer box 2 has concentric flow paths 8 for an inlet
6 and an outlet 7 that connects the upstream side and the
downstream side of the water supply piping respectively and,
in the midstream section 8b of said flow path 8, a drain port
9, which connects to the outside perpendicular to the flowpatch
8.
A valve port 10 is provided between the midstream section
8b and the downstream section 8c, and a valve seat 11 is provided
on the periphery of said valve port 10.
A sliding surface 12 is provided in the upstream section
8a to guide the inner tube member 3 and said sliding surface
12 has multiple grooves 13, 13a, ... formed equally spaced in
the circumferential direction on the circular inner face as
shown in Fig. S.
The inner cylinder member 3 is shaped to be substantially
cylindrical and fits into the upstream section 8a slidingly.
Its contact surface area against the inner tube member
3 is minimized by means of grooves 13, 13a, ... formed on the
sliding surface 12 in order to reduce the sliding resistance
against the inner tube member 3.
The reason that the inner surface (sliding surface 12)
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CA 02330002 2006-09-27
of the upstream section 8a is formed as described above instead
of forming multiple grooves on the outer surface of the inner
tube member 3 in order to decrease the sliding resistance of
the inner slide member 3 is that it would be necessary to
increase the thickness of the inner tube member 3 in order to
keep the strength of the inner tube member 3, which would in
essence increase the weight of the inner tube member 3, thus
negating the purpose of reducing the friction resistance, if
multiple grooves are formed on the outer circumference of the
inner tube member 3 or if the outer shape of the inner tube
member 3 is formed into a polygon.
The sliding surface 12 in the upstream section 8a in this
invention is formed as mentioned above and the outer shape of
the inner tube member 3 is formed to be cylindrical, maximizing
the resistance to external pressure, so that the inner tube
member 3 can be made relatively thin and light.
The outer circumference of the inner tube member 3 is
coated with Teflon further reducing the friction resistance
against said sliding surface 12, to minimize the sliding
resistance.
A diaphragm 14 is provided on the downstream side outer
circumference of the inner tube member 3 dividing the flow path
8 into an upstream section 8a and an area consisting of a
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CA 02330002 2001-01-02
midstream section 8b and a downstream section.
A relief valve 4 made of synthetic rubber is provided
on the end face of a downstream side opening of said inner tube
member 3.
This relief valve 4 is provided facing said valve seat
11 and is capable of moving toward or away from the valve seat
11 in accordance with the displacement of the diaphragm 14.
A relief valve spring 17 is provided between a small
diameter step 15 located on said opening and a cavity 16, which
is provided between the midstream section 8b and the downstream
section 8c, and the relief valve spring 17 energizes the relief
valve 4 toward valve opening direction.
A check valve 5 is formed substantially in a mushroom
shape having a spherical crown and provided inside the inner
tube member 3 to prevent fluid from flowing backward from the
downstream side. The check valve 5 is provided in such a way
as to be able to move toward or away from a check valve seat
19 located on the periphery of an upstream side opening of the
inner tube member 3, which essentially forms a check valve port
18.
The check valve 5 is supported by a guide ring 20, which
is provided to face the check valve seat 19 inside the inner
tube member 3.
CA 02330002 2001-01-02
The guide ring 20, as shown in Fig. 1, comprises: a ring
21 that surrounds the outer periphery across a small gap when
the check valve 5 is closed; multiple L-shaped support rods
22, 22a, ... that are provided on the downstream side end face
of said ring 21, equally spaced in the circumferential
direction thereof, and protruding toward the downstream side;
and a valve stem slide ring 23, which has a substantially
truncated cone-shape and is connected to the bent ends of said
support rods 22, 22a,
The spaces between the adjacent supporting rods 22, 22a,
... form the communicating openings 24, 24a, ... between the inner
tube member 3 and the midstream section 8b.
A valve stem 25 provided protrusively on the back of the
check valve 5 is inserted into the valve stem slide ring 23
slidingly and a check valve spring 28 is provided between an
annular cavity 26 provided around the valve stem 25 and a spring
catch 27 which is provided flange-like and protrusively on the
outer periphery of the base end of the stem slide ring 23,
wherein said check valve spring 28 energizes the check valve
in the valve closing direction.
Next, let us describe a modified version of the check
valve 5 referring to Figs. 6 through 9.
Fig. 6 is a plan view of the check valve 5, Fig. 7 is
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a front view, Fig. 8 is a bottom view, and Fig. 9 shows the
B-B cross section of Fig. 6.
The check valve 5 is formed to be substantially a mushroom
shape. It has a flat surface 30 formed on its face 29
confronting the check valve port 18, said surface having a
diameter smaller than the check valve port 18, and a conical
apex 31 formed in the middle of said flat surface 30.
Furthermore, multiple tilting grooves 33, 33a, ... having
a groove width decreasing gradually toward the center (valve
stem 27) of the back of the check valve 5 from the outer periphery,
which is further outside of a seating area 32 (area where the
valve contacts with the check valve seat 19 when it is closed)
provided outside of the flat surface 30 to correspond with the
check valve seat 19.
These tilting grooves 33, 33a, ... are equally spaced
(across small gaps S, Sl, ...) in the circumferential direction
on the check valve S.
The face 29 of the check valve 5 shown in Fig. 9 is formed
by coating synthetic rubber in a shape as described above.
Using the check valve 5 with such a shape, the water flow
splits into multiple radial flows from the apex 31 on the face
29 when the valve is open, while the flat surface 30 receives
the upstream side pressure to open fully instantaneously.
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CA 02330002 2001-01-02
As it opens fully, the flow increases and the flow path
from the outer periphery of the check valve 5 toward the
downstream side will be controlled by means of the tilting
grooves 33, 33a, ..., so that the water flow will be rectified
and flow along the shape of the check valve 5 toward the
downstream side.
It is also possible to control the pressure of the
midstream 8b of the water hammering prevention device 1 as
described below.
The dimensions of various parts of water hammering
prevention device 1 will be shown also using the Fig. 4.
In this scheme, the water hammering prevention device
1 is controlled to open the relief valve 4 to maintain the
pressure of the midstream section 8b always lower than the
upstream pressure by a margin of a constant value when it is
used within a certain application range of the upstream side
pressure.
More specifically, the object of holding a balance
between the valve closing pressure and the valve opening
pressure that applies to the relief valve 4 can be achieved
by choosing the effective diameter of the diaphragm 14 and the
valve seat diameter of the relief valve 4 to be approximately
equal (condition 1) and also by setting the spring loads of
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CA 02330002 2001-01-02
the relief valve spring 17 and the check valve spring 28 in
such a way as to maintain the pressure of the midstream section
Bb to be always lower than the upstream pressure by a margin
of a constant value (condition 2).
The condition 1 can be achieved by satisfying the
following equation:
A B C D (1)
where
A: Valve closing force applied to the relief valve as
the effective area of the diaphragm receives the upstream side
pressure
B: Valve opening force applied to the relief valve as
the area inside the internal periphery of the valve seat of
the relief valve receives the midstream pressure
C: Valve opening force applied to the relief valve by
the relief valve spring
D: Pressing force (sealing force) applied to the
relief valve (rubber) to close the relief valve
a: Friction resistance force generated in the internal
cylindrical member when the relief valve moves to open/close
the relief valve
Moreover, let:
Dl: Effective diameter of the diaphragm
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CA 02330002 2001-01-02
D2: Diameter of the valve seat (measured at the middle
of the seat width) of the relief valve
dl: Outer diameter of the valve seat of the relief valve
d2: Inner diameter of the valve seat of the relief valve
P1: Upstream pressure
P2: Midstream pressure (same as the downstream
pressure)
E: Coefficient for opening the relief valve from the
closed state (since E becomes smaller than the coefficient for
closing the valve from the open state, it is assumed to be 1)
OP: Pressure difference between the upstream side
pressure and the midstream pressure when the relief valve is
opened
F: Spring load of the relief valve spring
t: Thickness of the valve seat
Expressing the equation (1) using the above symbols, we get:
71 (D1/2)2Pl - 7c (D2/2)2 P2 - F = (7t(dl/2)2 - 7c (d2/2)2)P2E + a (1)'
Further, noting that:
P2 = Pl - AP
dl = D2 + t
d2 = D2 - t
and substituting the above into the equation (1)' above, we
get
CA 02330002 2001-01-02
(7tPl/4) (D 12 - D2 (D2 + 4t) ) = a - ( (7cAPD2 /4) (D2 + 4t) - F) (1) "
Therefore, by choosing the following conditions to hold
the equation (1)" true:
D1z = D2 (D2 + 4t) (2)
a = (7cOPD2/4) (D2 + 4t) - F (3)
we learn that the balance between the valve opening pressure
and the valve closing pressure applied on the relief valve 4
can be maintained always without being affected by changes in
the upstream pressure Pl.
Since D2 >> t, and D12 = D2 (Dz + 4t) , we get D1 = D2.
The condition 2 is to maintain the relief valve 4 closed
under normal conditions (water running or stopped) and it
requires that the water pressure of the water running through
after the pressure reduction due to the check valve spring 28
has to be greater than the pressure of the midstream 8b.
This condition 2 can be expressed in the following
equation:
OPl > AP + Pa + Pb (4)
where,
OP1: Pressure difference between the upstream side
pressure and midstream section pressure caused by the check
valve spring
AP: Pressure difference between the upstream side
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CA 02330002 2001-01-02
pressure and midstream section pressure when the relief valve
is opened
Pa: Pressure difference between the upstream side
pressure and midstream section pressure caused by the relief
valve spring
Pb: Minimum pressure required for closing the relief
valve (AP - OP1)
Moreover, let:
x: Diameter of the valve seat (measured at the middle
of the seat width) of the check valve
D2: Diameter of the valve seat (measured at the middle
of the seat width) of the relief valve
F: Spring load of the relief valve spring
f: Spring load of the check valve spring
then, the equation (4) can be rewritten as:
OP1 > AP + Pa +(OP - OP1) , or
2 f / (Tc (x/2)2) > 2AP + F/ (iT (D2/2)2) (4) 1
An appropriate combination of spring loads F and f of
the relief valve spring 17 and the check valve spring 28 is
selected based on the above equation for satisfying the
condition 2 to set the relief valve spring 17 and the check
valve spring 28 respectively.
Let the diameter of the valve seat (measured at the middle
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CA 02330002 2001-01-02
of the seat width) of the relief valve 4 be, D2 = 10.95 cm,
the diameter of the check valve seat 19 (measured at the middle
of the seat width) be, x = 5 cm, the thickness of the valve
seat 11 of the relief valve 4 be, t = 0.1 cm, and the desired
=
pressure difference for opening the relief valve 4 be, AP
kPa.
Using the equation (2),
The effective diameter of the diaphragm 14, D1r was
calculated to be 11.15 cm.
Based on the equation (4)', the relief valve spring 17
and the check valve spring 28 were selected to satisfy the
following:
spring load of the relief valve 17, F 24.5 N
spring load of the check valve 28, F 39.2 N
From the above equation (3), the friction resistance
force a is calculated to be 71.15 N.
When a water hammering prevention device 1 was used and
the upstream pressure P1 was changed from 0.1 to 1 MPa, the
valve opening pressure difference AP of the relief valve 4 was
approximately 10 kPa in average.
Therefore, this water hammering prevention device 1 was
able to maintain the pressure of the midstream section 8b to
be always lower than the upstream side pressure P-~y by a margin
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CA 02330002 2001-01-02
AP of a constant value (approximately 10 kPa).
Next, let us describe an example piping of the water
hammering prevention device 1 with reference to Figs. 10 and
11.
Fig. 10 is a schematic drawing of a elevated tank type
water supply device 34.
The drawing shows a water receiving tank 35, to which
main water piping 36 is connected. Said water tank 35 is
connected to an elevated tank 41 on the rooftop of a building
40 via a lifting pipe 39 as well as a lifting pump 37 and a
check valve 38. From the lifted tank 41, water supply piping
42 connects to faucets 43, 43a, etc.
The water hammering device 1 is connected in parallel
to said check valve 38, i.e., its inlet port 6 and outlet port
7 are connected to the lifting pipe 39 on the upstream and
downstream sides of the check valve 38 respectively, and its
drain port 9 is connected to said water receiving tank 35 via
piping.
The drain port 9 secures a specified drain port space
(gap) as it connects to a drain path 44 so that water will be
indirectly drained by gravity to the receiving tank 35.
In the water supply device 34, it also becomes possible
to abolish the check valve 38 and install the water hammering
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CA 02330002 2001-01-02
prevention device 1 in the same place as the check valve 38.
In this case, the inlet port 6 and the outlet port 7 of
the water hamming prevention device 1 are connected in the
middle of the lifting pipe 39, one at the upstream side and
the other at the downstream side respectively, and the drain
port 9 is connected to the water receiving tank 35.
Although the piping example for the water hammering
prevention device 1 is shown for the elevated tank type water
supply device 34, the water hammering prevention device 1 can
be connected in the middle of the piping where water hammering
occurs with the drain port 9 being connected to the water
receiving tank in other types of water supply devices.
Fig. 11 is a schematic drawing of a high pressure water
injection water supply device 45 installed in manufacturing
plants and other work places for the purpose of washing various
things.
This water supply device 45 has a water receiving tank
47, to which a main water piping 46 is connected. From the
tank, a water supply pipe 50 extends to a turbine pump 48 and
a check valve 49, and eventually to high pressure water
injection guns 51, 51a, ..., which are terminal equipment
provided at each end of the pipe.
A water hammering prevention device 1 is installed in
CA 02330002 2001-01-02
the water supply piping 50 in such a way as to be connected
in series with each high pressure water injection gun 51, 5la,
etc.
The inlet port 6 and the outlet port 7 of the water
hammering prevention device 1 are connected to the upstream
side and the down stream side of the water supply piping 50,
and the drain port 9, similar to that shown before, which secures
a specified drain port space as it connects to drain path 52
so that water will be indirectly drained outside by gravity;
as an alternative, said drain paths 52, 52a, ... can be connected
via piping (not shown) to the water receiving tank 47.
Next, let us describe the operation of the water hammering
prevention device 1 referring to Figs. 1 through 3, 10 and 11.
When water is not running, the relief valve 4 and the
check valve 5 are both closed as shown in Fig. 1.
When water is running, as shown in Fig. 2, the relief
valve 4 is closed due to the upstream side pressure similar
to the case when water is not running, and the check valve 5
is opened. In case of the water supply systems 34 and 45 shown
in Figs. 10 and 11, water is supplied either to faucets, 43,
43a, etc. , or high pressure water inj ection guns 51, 51a, etc. ,
which are respective terminal equipment.
When a water hammering action occurs in the downstream
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side of the water hammering prevention device 1 as in the case
of closing the faucets 43, 43a, ... or high pressure water guns
51, 51a, ..., the downstream side pressure (reverse pressure)
becomes higher than the upstream side pressure, so that, as
shown in Fig. 3, the check valve 5 closes and reverse pressure
is applied to the relief valve 4 opposing the valve closing
pressure, so that the relief valve 4 will be pressed in the
upstream direction to cause it open, and the midstream section
8b communicates with the drain paths 44, 52, 52a, ... via drain
port 9 to drain the pressurized fluid.
Thus, the reverse pressure is drained to the outside and
the water hammering action is prevented.
When the reverse pressure disappears and the downstream
side pressure becomes lower than the upstream side pressure,
or, in the case where the midstream section 8b is pressure
controlled as mentioned before, the pressure difference
between the upstream side pressure and the midstream section
pressure (same as the downstream side pressure) returns to the
preset value, the relief valve 4 closes.
The water, which is drained when the relief valve 4 opens,
is returned to the water receiving tank 35 via the drain path
44 in the case of the water supply device 34, and is drained
by gravity in the case of the water supply device 45 or returned
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to the water receiving tank 47 in the alternative case where
the drain path 52 is connected via piping to the water receiving
tank 47.
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