A differential-pressure valve is described including a valve passageway formed through a fixed wall and closable by a valve member displaceable by a differential-pressure sensor biassed to close the valve passageway and subjected to the differential pressure such that the higher pressure tends to open the valve passageway and the lower pressure tends to close the valve passageway. The valve further includes an annular sealing surface between the sensor and the fixed wall through which the valve passageway is formed, which sealing surface circumscribes the valve passageway such that when the sensor is in its closed position, the annular sealing surface seals off a portion of the high-pressure face of the sensor from the high-pressure thereby increasing the differential pressure required to actuate the sensor to open the valve passageway, and when the sensor is in its open position the annular sealing surface exposes said portion of the high-pressure face of the sensor to the high-pressure thereby decreasing the differential pressure required to actuate the sensor to close the valve passageway.

BACKGROUND OF THE INVENTION 
The present invention relates to a differential-pressure valve, and also to 
a valve system including a controlled device, such as a main valve, 
controlled by the differential-pressure valve. 
There are many applications in which differential-pressure valves are used 
to control other devices, such as main valves, in accordance with the 
difference in pressure at two locations of the device. One such 
application which may be mentioned for purposes of example is in 
backwashable filtering devices which are automatically actuated to 
backwash the filter whenever a predetermined quantity of dirt has 
accumulated on the filter. In such an application, the backwashing 
operation is automatically initiated by sensing the difference in the 
pressure at points upstream and downstream of the filter body, and when 
the pressure differential reaches a predetermined level, a valve is opened 
to initiate the backwashing of the filter. As the filter body is thus 
cleaned during the backwashing operation, the pressure-drop across it 
becomes lower thereby lowering the differential pressure; this is also 
sensed by the sensor which terminates the backwashing operation by closing 
the valve when the differential pressure reaches a predetermined minimum 
value. Examples of such backwashable filtering devices are described in my 
prior patent applications Ser. No. 74,525, filed Sept. 11, 1979, and Ser. 
No. 92,583, filed Nov. 8, 1979. 
Such differential-pressure valves commonly include a valve passageway 
formed through a fixed wall and closable by a valve member displaceable by 
a differential-pressure sensor biassed to close the valve passageway and 
subjected to the differential pressure such that the higher pressure tends 
to open the valve passageway and the lower pressure tends to close the 
valve passageway. 
An object of the present invention is to provide a differential-pressure 
valve of the above type but including an improved construction having a 
number of advantages as will be described more particularly below. 
BRIEF SUMMARY OF THE INVENTION 
According to a broad aspect of the present invention, there is provided a 
differential-pressure valve of the foregoing type, characterized in that 
the valve further includes an annular sealing surface between the sensor 
and the fixed wall through which the valve passage is formed, which 
sealing surface circumscribes the valve passageway. Further, the 
high-pressure face of the sensor has fixed thereto the valve member 
movable to open and close the passageway, and has also fixed thereto the 
mentioned annular sealing surface circumscribing the valve member. The 
arrangement is such that when the sensor is in its valve-closed position, 
the annular sealing surface seals off a portion of the high-pressure face 
of the sensor from the high-pressure thereby increasing the differential 
pressure required to actuate the sensor to open the valve passageway, and 
when the sensor is in its valve-open position the annular sealing surface 
exposes said portion of the high-pressure face of the sensor to the 
high-pressure thereby decreasing the differential pressure required to 
actuate the sensor to close the valve passageway. 
The above features impart a quick-action, bistable-operation to the valve, 
in that the valve member is stably held closed until the predetermined 
opening differential-pressure is reached at which time it starts to open, 
whereupon the annular sealing surface is broken thereby increasing the 
cross-sectional area of the sensor subjected to the high pressure and 
causing the sensor to move with a quick action to its open position. 
Another advantage in the above-described construction is that the 
differential pressure required to close the valve is less than that 
required to open the valve. This is highly desirable in many applications 
of differential-pressure valves. For example, in the above-mentioned 
application wherein the differential-pressure valve is used to effect a 
backwashing of the filter body, it is desirable to initiate the 
backwashing operation when a predetermined pressure differential has been 
reached (e.g., 0.5 atmosphere) and to continue the backwashing operation 
until a smaller pressure differential (e.g., 0.1 atmosphere) has been 
reached to assure that the filter body is substantially clean before the 
backwashing operation is terminated. This operation is inherent in the 
differential-pressure valve of the present invention since the 
high-pressure face of the sensor is of larger cross-sectional area when 
the valve is open then when the valve is closed, thereby requiring a lower 
pressure differential to close the valve than to open it. 
According to another aspect of the invention, there is provided 
fluid-pressure controlled apparatus including a differential-pressure 
valve as described above, and a device controlled thereby, the controlled 
device including a cylinder having a piston movable therein to define a 
pressurized chamber, said valve passageway of the differential-pressure 
valve being connected to the pressurized chamber for controlling the 
pressure therein. 
In the preferred embodiment of the invention described below, the 
controlled device is a main valve including a second piston movable in a 
second cylinder whose wall is formed with the main valve passageway, the 
second piston being of smaller cross-sectional area than the 
first-mentioned piston and being biassed to the closed position of the 
main valve by a spring. Such a construction is particularly useful in the 
automatically-back-washable filters mentioned above, since it assures that 
the main valve passageway, which is opened to effect the backwashing 
operation, will remain closed until the pressure within the line in which 
the filter is used builds up to the normal operating pressure. Such an 
arrangement obviates the need for separate pressure-regulators, or other 
devices, which are commonly included in the existing arrangements to 
assure that the main valve, which is opened by the pressure differential 
to initiate the backwashing operation, remains closed until the line has 
come up to the operating pressure, e.g., when initially filling the line. 
Further features and advantages of the invention will be apparent from the 
description below.

The valve device illustrated in the accompanying drawing is for use in 
displacing a piston 2 movable within a cylinder 4 for opening or closing a 
valve passageway 6 in accordance with the difference in pressure between a 
high-pressure source P.sub.H and a low pressure source P.sub.L. 
One application for such a device, as mentioned above, is in a backwashable 
filter such as described in my above-cited prior patent applications, 
wherein piston 2 is subjected to the pressure in chamber 8 at the upstream 
side of the filter body so as to move (leftwardly in the drawing) to 
uncover opening 6, and thereby to permit the filter to be backflushed 
through opening 6. In such an application, the high pressure source 
P.sub.H is that at the upstream side of the filter body, and the low 
pressure source P.sub.L is that at the downstream side of the filter body. 
Thus, when the filter body is relatively clean, there will be a small 
pressure-drop through it, so that the pressure differential P.sub.H 
-P.sub.L will be very small, insufficient to actuate valve member 2 to 
open passageway 6. However, as the dirt accumulates on the filter body, 
the pressure differential P.sub.H -P.sub.L increases, such that when a 
predetermined pressure differential is reached, valve member 2 is actuated 
to uncover passageway 6 and thereby to initiate the backwashing operation. 
The differential-pressure sensor which automatically controls the actuation 
of valve member 2 includes a diaphragm 10 of circular shape mounted 
between a pair of housing sections 12 and 14 secured together by bolts 16. 
The sensor further includes a circular rigid disc 18 secured within a 
central opening formed through the diaphragm 10 by means of a plastic cap 
20 threaded onto exterior threads formed on stem 22 of the circular disc. 
The circular disc 18 carries a rod-shaped valve member 24 movable in or 
out of a control valve opening or passageway 26 formed in an end wall 28 
integral with housing section 12. 
The high pressure source P.sub.H is inletted, via port 30 formed in housing 
section 12, into a high-pressure chamber 32 at one side of the sensor 
diaphragm 10 such that the high-pressure P.sub.H tends to move valve 
member 24 carried by the diaphragm to open valve passageway 26. The 
low-pressure source P.sub.L is inletted, via port 34 formed in housing 
section 14, into a low-pressure chamber 36 at the opposite side of the 
sensor diaphragm 10 such that the low-pressure tends to move valve member 
24 carried by the diaphragm to close the valve passageway 26. 
In addition, a coil spring 38 is provided to bias the sensor diaphragm 10 
to the closed position of its valve member 24 with respect to valve 
passageway 26. More particularly, spring 38 is received within a cavity 
formed centrally of stem 22 of the circular disc 18 and bears against a 
piston 40 having a stem 42 threadedly received within an opening in end 
wall 44 of housing section 14. Stem 42 includes a rotatable external knob 
46 permitting piston 42 to be displaced inwardly or outwardly to preset 
the force applied by spring 38 against the sensor diaphragm 10, and 
thereby to preset the operating points of the valve. 
End wall 28 formed in housing section 12 includes an annular flange 50 
threadedly received on housing section 52. The latter housing section is 
in turn threadedly received within the previously-mentioned housing 
section 4 containing the main valve member 2 and the main valve passageway 
6. 
As mentioned above, the main valve member 2 is in the form of a piston 
movable within housing section 4, serving as a cylinder. Piston 2 is 
connected by a stem 54 to another piston 56 movable within housing section 
52, which also serves as a cylinder. A spring 57, interposed between 
piston 2 and an internal shoulder 58 formed on housing section 52, urges 
piston 2, and thereby piston 56, in the direction (rightwardly in the 
drawing) tending to decrease the volume of chamber 8. 
End wall 28, through which is formed the control valve passageway 26, is 
common to the high-pressure chamber 32 of the differential-pressure 
sensor, and chamber 59 defined by the end wall and piston 56 movable 
within cylinder 52. Chamber 59 is connected to the high-pressure chamber 
32 at the opposite side of end wall 28 by a small bore 60 formed through 
end wall 28, this bore (e.g., 1 mm) being considerably smaller in 
cross-sectional area than that of the control valve passageway 26 (e.g., 3 
mm). 
Valve passageway 26 is formed in a dished central part of end wall 28 and 
is lined with an O-ring 62 adapted to sealingly engage the rod-shaped 
valve member 24 when the latter is in its closed position. The movement of 
valve member 24 is guided by a guide ring 64 carried on the opposite face 
of end wall 28 and formed with an opening for guiding the movement of the 
valve member 24 but permitting some clearance with respect thereto; that 
is, the rod-shaped valve member 24 is not sealingly received within guide 
rod 64. 
An O-ring 70 is received within a circular recess formed on the inner face 
(i.e., the face exposed to the high-pressure chamber 32) of the circular 
disc 18. O-ring 70 is of larger diameter than, and circumscribes, both the 
guide ring 64 carried by the end wall 28, and the valve passageway 26 
formed through the dished portion of the end wall. 
The arrangement is such that when the sensor diaphragm 10 is in the 
valve-closed position as shown in the drawing (i.e., with its valve member 
24 received within valve passageway 26), the O-ring 70 forms an annular 
sealing surface between the sensor diaphragm 10 and end wall 28. This 
seals off that portion 72 of the high-pressure face of the diaphragm 
sensor 10, enclosed by O-ring 70, from the high-pressure within chamber 
32, thereby increasing the differential pressure (P.sub.H -P.sub.L) 
required to actuate the sensor diaphragm 10 to move its valve member 24 
out of the valve passageway 26 to open the valve. On the other hand, when 
the sensor diaphragm 10 is in the valve-open position, this portion 72 of 
the high-pressure face of the sensor diaphragm is exposed to the 
high-pressure in chamber 32, thereby decreasing the differential pressure 
required to move the diaphragm to its closed position. The foregoing will 
be better understood from the description below of the operation of the 
device. 
Space 72 within the O-ring 70 communicates, via the above-mentioned 
clearance between the guide ring 64 and the valve member 24, with a space 
74 on the opposite side of the guide ring. The latter space is in turn 
vented to the atmosphere via a bore 76 formed radially through end wall 
28. 
The device illustrated in the drawings may be used in the following manner 
for opening or closing valve passageway 26 in response to a predetermined 
difference in pressure between the high pressure source P.sub.H and the 
low pressure source P.sub.L. 
First, the differential-pressure for opening the valve passageway 26 may be 
preset by rotating the external knob 46 which adjusts the position of 
piston 40, and thereby the force spring 38 exerts against the sensor 
diaphragm 10 towards the closing position of valve member 24. However, as 
mentioned above and as to be described more particularly below, the 
differential-pressure P.sub.H -P.sub.L for opening the valve will be 
significantly higher than that for closing the valve because of the 
presence of the annular sealing surface by the O-ring 70 when the sensor 
diaphragm is in its closed position. 
Next, the high-pressure source P.sub.H is connected to inlet 30 whereby 
chamber 32 on one side of the sensor diaphragm 10 will be pressurized to 
that of the high-pressure source P.sub.H ; and the low-pressure source 
P.sub.L is connected to port 34 whereupon chamber 36 on the opposite side 
of the sensor diaphragm will be pressurized to that of the low-pressure 
source P.sub.L. 
Assuming that the sensor diaphragm 10 is in the illustrated valve-closed 
position, it will be seen that O-ring 70 will engage the confronting face 
of end wall 28, thereby sealing the surface area of the sensor diaphragm 
10 within space 72 enclosed by the O-ring from the high-pressure of 
chamber 32. This reduces the force applied by the high-pressure chamber 32 
to that side of the diaphragm tending to move it to the valve-open 
position. Accordingly, the pressure within the low-pressure chamber 36 
will have to drop substantially before the pressure difference between the 
two pressure sources P.sub.H and P.sub.L will be sufficient to cause the 
sensor diaphragm 10 to move (leftwardly) to displace its valve member 24 
out of the valve passageway 26, thereby opening the valve. However, as 
soon as the diaphragm has started to move in the valve-opening direction, 
the O-ring 70 moves with it away from the face of end wall 28. This 
exposes an enlarged surface area (i.e. enlarged by the area within the 
O-ring) of the face of the sensor diaphragm subjected to the high-pressure 
of chamber 32, whereupon the enlarged force effects a fast acting opening 
of the valve member 24 with respect to the valve passageway 26. 
When the illustrated device is used for controlling the backwashing of a 
filter (in the application briefly mentioned above), the high-pressure 
source P.sub.H would be connected to a point upstream side of the filter 
body, and the low-pressure source P.sub.L would be connected to a point 
downstream of the filter body. Thus, the pressure differential applied to 
the sensor diaphragm 10 would be a measure of the quantity of dirt 
accumulated on the filter body, the pressure differential being high when 
the quantity of dirt is large and low when the quantity of dirt is small. 
When the sensor diaphragm 10 is in its closed position with its valve 
member 24 closing the valve passageway 26, the high-pressure in chamber 32 
is transmitted via bore 60 into chamber 59, thereby pressurizing that 
chamber and causing piston 56 to move rightwardly, whereby piston 2 would 
be in the illustrated closed position with respect to the main valve 
passageway 6. 
It may be noted in this connection that whereas the high-pressure upstream 
of the filter body is also applied to piston 2 in chamber 8, tending to 
move the piston leftwardly to open the main valve passageway 6, the 
surface area of piston 56 is larger than that of piston 2 so that a 
greater force is applied against piston 56 moving it to the illustrated 
position wherein piston 2 closes the main valve passageway 6. 
Now, as dirt accumulates on the filter body, the pressure within the 
high-pressure chamber 32 remains constant, but that within the 
low-pressure chamber 36 drops, until the pressure differential between the 
two chambers, as applied to the sensor diaphragm 10, moves the diaphragm 
leftwardly as described above, causing it to withdraw its valve member 24 
from valve passageway 26. This releases the pressure within chamber 59 via 
passageway 26 and bore 48, causing the high-pressure in chamber 8 to move 
piston 2 leftwardly to uncover the main valve passageway 6 which initiates 
the backwashing operation, the dirty water being flushed out through 
passageway 6. 
As the filter body is cleaned during the backwashing operation, the low 
pressure P.sub.L downstream of the main filter body increases, thereby 
reducing the pressure differential between P.sub.L and P.sub.H. However, 
since the high-pressure face of the sensor diaphragm 10 is now subjected 
to the high-pressure over its complete face, including that within the 
O-ring 70 as described above, the diaphragm will remain in its open 
position until the pressure within chamber 36 builds up to the point 
wherein the force applied by it to the sensor diaphragm 10, in combination 
with the force applied by spring 38, overcomes the enhanced force applied 
in the opposite direction to the diaphragm by the pressure within the 
high-pressure chamber 32. When this occurs, the sensor diaphragm 10 moves 
(rightwardly) to bring its valve member 24 into valve passageway 26, 
thereby closing the latter passageway with respect to bore 76. The 
pressure within chamber 59 then builds up by the high-pressure applied 
thereto from chamber 32 via bore 70, until piston 56 is moved rightwardly, 
to cause piston 52 also to move rightwardly and to close the main valve 
passageway 6, thereby terminating the backwashing operation. 
As diaphragm 10 is displaced during the closing operation, its O-ring 70 
again engages the face of end wall 28, thereby again sealing the space 72 
within the O-ring from the high-pressure of chamber 32. This reduces the 
area of the face of diaphragm 10 subjected to the high-pressure in chamber 
32, thereby reducing the force applied by this high pressure to the 
diaphragm opposing the closing force applied by the low-pressure vhamber 
36. A quick and positive closing action of the valve member 24 is thus 
produced during the final closing movement of valve member 24. 
As one example, the arrangement may be such that valve member 24 opens at a 
differential pressure of about 0.5 atmosphere and closes at a 
differential-pressure of about 0.1 atmosphere to assure that the filter 
body will be substantially clean before the backwashing operation is 
terminated. The above opening and closing operating points of the sensor 
may be pre-fixed by suitably selecting the diameter of the O-ring 70 
(which determines the proportion of the high-pressure face of diaphragm 10 
is made ineffective when the valve member is closed), and by adjusting 
knob 46 (which determines the force applied by spring 38 against the 
diaphragm). 
Another advantage in the device illustrated, particularly when used for 
controlling the backwashing operation of a filter, resides in the 
provision of spring 57 and the relative dimensions of the two pistons 8 
and 56. These features assure that until the pressure P.sub.H (namely, the 
line inlet pressure or the pressure upstream of the filter body) has built 
up to the normal operating pressure, piston 2 will be in the illustrated 
closed position with respect to the main valve passageway 6 so as to 
prevent the initiation of the backwashing operation until the pressure 
within the line has built up to the operating pressure, at which time the 
differential-pressure sensor, which opens or closes the valve passageway 
26, will control the initiation and the termination of the backwashing 
operation as described above. This arrangement thus avoids the sensitivity 
of the system to the line pressure and obviates the need for a separate 
pressure regulator or other device for maintaining the main valve member 2 
in its closed position with respect to passageway 6 (e.g., during filling 
of the line) until the line pressure has built up to its operating level. 
While the invention has been described with respect to one preferred 
embodiment, it will be appreciated that many variations and other 
applications of the invention may be made. For example, O-ring 70 may be 
mounted on end wall 48, rather than on the sensor diaphragm 10, in which 
case the annular sealing surface circumscribing the control member 24 
would be the face of the circular disc 18 of the diaphragm 10 engaged by 
the O-ring in the valve-closed position of the diaphragm. Further, the 
differential-pressure sensor could be of the piston type, rather than of 
the diaphragm type. Also, spring 57 could be applied between the end wall 
48 and piston 56 rather than in the position illustrated. In addition, the 
differential-pressure sensor could also be used for controlling many other 
types of valves or fluid devices. Many other variations, modifications and 
applications of the illustrated embodiment will be apparent.