JPH0124951B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a valve device in which a main valve itself equipped with a low flow adjuster (regulating valve) performs two-stage opening and closing, and in which a pilot type constant flow control valve performs constant flow control.

Generally, in a fixed-rate liquid supply system that supplies liquid to tanker trucks at a liquid supply station, a flowmeter and a metering valve (open at the start of liquid supply and receive a signal from the flowmeter when the desired amount is reached) are installed in the liquid supply line in sequence. A constant flow valve (which always flows at a constant flow rate), and a loading arm (which is inserted into the lorry tank) are provided. Here, as a constant flow valve, there is a type having a function as a constant flow valve that allows a constant flow to flow through the liquid supply line at all times, in addition to the function of communicating and blocking the liquid supply line.

This conventional valve device is shown in FIG. In the figure, a valve body 2 of a valve device 1 has a main valve seat 2a, and a main valve body 3 fitted into a cylindrical body portion 2b is seated on the main valve seat 2a by a spring 4. The main valve seat 2a and the main valve body 3 constitute a main valve 5 (interposed in the middle of the liquid supply line 51), thereby defining a primary chamber 2c and a secondary chamber 2d. The main valve body 3 has a central hole 3a, an auxiliary valve seat 3b, flow paths 3c, 3d, and a pressing rod portion 3e.
The auxiliary valve body 6 fitted into the auxiliary valve seat 3 is moved by the spring 7 to the auxiliary valve seat 3.
He is seated on b. Auxiliary valve seat 3b and auxiliary valve body 6
constitutes the auxiliary valve 8. Reference numeral 9 denotes a manifold, which has a plurality of valves and flow paths inside, and is connected to the piping line 10a.
~10d to the primary chamber 2c, secondary chamber 2d, respectively.
It is connected to the main valve upper chamber 2e and the auxiliary valve upper chamber 2f.

Reference numeral 52 denotes a pilot type constant flow control valve, which includes a diaphragm membrane 53 (in which upper and lower chambers 52a and 52b are defined), a plunger 54 (having a flow path 54a) that is integrally displaced with the diaphragm membrane 53, and a small valve 55 (small valve seat 54b). ,
It has a small valve body 56) and is attached to the upper part of the valve body 2. The upper and lower chambers 52a and 52b are communicated with the liquid inlet side of the flow meter 57 of the liquid supply line 51 and the primary chamber 2c via piping lines 58a and 58b, respectively. The main valve 3 determines its opening degree by following the vertical movement of the plunger 54 while keeping the upper end of its pressing rod portion 3e in contact with the small valve body 56.

At the start of liquid supply, when the manifold 9 operates to release the liquid in the auxiliary valve upper chamber 2f to the secondary chamber 2d via the flow path 3d and lines 10a and 10b to reduce the pressure, the auxiliary valve body 6 resists the spring 7. The auxiliary valve 8 opens and the liquid in the primary chamber 2c flows into the flow path 3.
c, it begins to flow to the secondary chamber 2d side via the auxiliary valve 8 (one step open (half open) state). Next, line 10c, 1
The liquid in the main valve upper chamber 2e is transferred to the secondary chamber 2d via 0b.
When the pressure is reduced, the main valve body 3 moves upward in the same way, the main valve 5 opens, and the liquid flows to the secondary chamber 2d via the main valve 5 and the auxiliary valve 8 (two-stage opening). (fully open state).

Next, at the end of liquid supply, the liquid on the primary chamber 2c side is led to the main valve upper chamber 2e through the lines 10a and 10c, and the main valve 5 is closed (one-stage closed (half-closed)), contrary to the above case. state), lines 10a, 10d,
The primary chamber 2c is connected to the auxiliary valve upper chamber 2f via the flow path 3d.
The liquid on the side is guided, and the auxiliary valve 8 is closed (two-stage closed (fully closed) state).

In addition, in the above-mentioned two-stage open (fully open) state, the control valve 5
2 is the inflow side and outflow side of the flowmeter 57 (primary chamber 2
The hydraulic pressures of c) are introduced through lines 58a and 58b, respectively, and the differential pressures therebetween are detected. Therefore, for example, when the supply pressure of the liquid supply line becomes high and the liquid flow rate increases from a preset constant flow rate, the differential pressure across the flow meter 57 becomes larger than a predetermined value, and the diaphragm membrane 5
3 and plunger 54 are pushed down. As a result, the small valve body 56 is relatively pushed up against the pressing rod portion 3e to open the valve, and the hydraulic pressure of the primary chamber 2c is introduced into the main valve upper chamber 2e via the line 58b.
Therefore, the main valve element 3 moves downward due to this increase in hydraulic pressure and the biasing force of the spring 4, gradually reducing the valve opening of the main valve 5, reducing the flow rate, and gradually decreasing the differential pressure. When the above differential pressure returns to the predetermined value, the main valve body 3
The pressing rod 3e presses the small valve body 56 against the small valve seat 54b.
The valve is slightly opened to reach a position where the amount flowing into the main valve upper chamber 2e and the amount flowing out through the line 10c are balanced, and the valve opening degree of the main valve 5 is adjusted to an appropriate state and the flow rate is returned to the set flow rate. urge

Conversely, when the supply pressure of the liquid supply line becomes low and the liquid flow rate decreases below the set flow rate, the differential pressure becomes smaller than the predetermined value and the plunger 54 moves upward. Therefore,
Due to the action of the manifold 9, the hydraulic pressure in the main valve upper chamber 2e is released through the line 10c, and the main valve body 3 moves upward following the plunger 54, and the differential pressure reaches a predetermined value as in the above case. At the time of return, balance is established and the flow rate is returned to the set flow rate.

However, according to the above conventional example, two valves, the main valve 5 and the auxiliary valve 8, are required as valves for the supply liquid to pass through, and the control liquid passage is also complicated, requiring a dedicated manifold 9. However, since the control valve 52 is integrally attached to the valve body 2, the control valve 52 is difficult to control when the constant flow function is not required for the valve device 1. When valve 52 is removed,
There is a drawback that a lid is required to close the upper part of the upper chamber 2e of the valve body, which is inconvenient in use. both,
There was a drawback that the structure of interlocking the plunger 54 (small valve 55) and the pressing rod portion 3e was troublesome.

The present invention simplifies the overall configuration and operation by providing only the main valve as the valve through which the supply liquid passes, as well as a low flow adjuster (adjusting valve) for controlling hydraulic pressure and two communication passage opening/closing means. To provide a valve device that reduces costs, provides a pilot type constant flow control valve separately from a valve body of a main valve, improves convenience of use, and simplifies the configuration and operation of the control valve itself. With the goal.

The configuration for this purpose includes a valve body disposed in the liquid supply line, a first valve seat, and a first valve seat that can freely move toward and away from the valve body.
a diaphragm membrane fixed between the valve body and the first valve body in a primary chamber of the main valve and defining a diaphragm chamber; the diaphragm chamber and the main valve; a first communication path that communicates with the secondary side of the valve; a second valve seat disposed in the middle of the first communication path; and a second valve seat that faces the second valve seat and is integral with the first valve body. an adjusting valve including a second valve body that seats on the second valve seat when the first valve body is displaced and moves a predetermined amount in the valve opening direction; a first communication passage opening/closing means; a second communication passage communicating between the primary side of the main valve and the diaphragm chamber; and a third communication passage communicating between the diaphragm chamber and the secondary side of the main valve. , a throttle disposed in the middle of the second communication passage, a second communication passage opening/closing means disposed in the middle of the third communication passage, and a throttle disposed in the middle of the third communication passage; By introducing the hydraulic pressure at a predetermined location as a pilot pressure and making the valve opening degree of the control valve variable variable to control the flow rate of the third communicating path,
It consists of a pilot-type constant flow control valve that makes the flow rate of the liquid supply line constant.

Next, one example will be described.

FIG. 2 is a longitudinal sectional view of an embodiment of the valve device according to the present invention.

In the figure, the valve device 11 has the functions of both a fixed quantity valve and a constant flow valve, and includes a valve body 12 and a lid body 1.
3, the valve body 12 has a main valve seat 12a, a primary chamber 1
2b (hydraulic pressure P ₁ ), and a secondary chamber 12c (hydraulic pressure P ₂ ),
It is interposed at a position downstream from the flow meter 62 in the middle of the liquid supply line 61.

14 is the main valve body and the main valve shaft 1 is integrally provided with this body.
5 is fitted and guided into an outer cylinder 25, which will be described later, so that it can freely move up and down, and is supported by being biased downward by a spring 16, and is seated on the main valve seat 12a. The main valve seat 12a and the main valve body 14 constitute a main valve 17. As shown in FIG. 3, a shaft 18 is screwed into the upper end of the main valve shaft 15 and fixed thereto, and a ring-shaped poppet 19 fitted onto the shaft 18 so as to be movable up and down is urged upward by a spring 20 and pressed into contact with a retaining ring 21. has been done.

22 is a diaphragm membrane, the peripheral part of which is the valve body 12
and the lid body 13, and the central part is fixed to the main valve body 14 by a diaphragm retainer 23, and a diaphragm chamber 12d (hydraulic pressure
P ₃ ).

24 is a low flow adjuster (Low Flow
The adjuster is roughly composed of an outer cylinder 25, a guide rod 31, and the poppet 19, and the guide rod 31 is screwed into the upper part of the outer cylinder 25 and the lock nut 32
Fixed by The outer cylinder 25 is inserted and fixed to the upper part of the lid body 13 via the mounting plate 33. At this time, the main valve shaft 15 is coaxially fitted into the lower part of the outer cylinder 25, and the poppet 19 is spaced apart and opposed to the valve seat 31b at the lower end of the flow path 31a of the guide rod 31. The valve seat 31b and the poppet 19 constitute a regulating valve 34, and the diaphragm chamber 1
2d is connected to a piping line 38, which will be described later, through a hole 25a of the outer cylinder 25, a flow path 25b, a regulating valve 34, a flow path 31a, and a hole 25b. Also 35, 36,
37 are O-rings for sealing.

38 is a piping line as a first communication passage, which communicates the hole 25b of the outer cylinder 25 and the secondary chamber 12c, and a solenoid valve 3 as a means for opening and closing the first communication passage is installed in the middle of the piping line.
It has 9.

A piping line 40 communicates with the diaphragm chamber 12d, and its ends communicate with the primary chamber 12b and secondary chamber 12c via piping lines 41 and 42, respectively.
The lines 40 and 41 constitute a second communication path 43,
A throttle 44 is provided in the middle of the line 41, lines 40 and 42 constitute a third communication path 45, and a solenoid valve 46 is provided in the middle of the line 42 as a means for opening and closing the second communication path.

Reference numeral 63 designates a pilot type constant flow control valve, which controls the upper chamber 63a (hydraulic pressure _P4 , spring 64) by a diaphragm membrane 65.
A lower chamber 63b (having a hydraulic pressure P ₅ ) is defined below the partition wall 63c, and a primary flow path 63d and a secondary flow path 63 are formed below the partition wall 63c.
e, has a valve seat 63f. A control valve body 66 integral with the diaphragm membrane 65 fits into the partition wall 63c and corresponds to the valve seat 63f, thereby forming control valve portions 67, 63f, and 66. This control valve 63 is interposed in the middle of the line 42 of the third communication path 45, and furthermore, the upper and lower chambers 63a, 6
3b are connected to the primary chamber 1 by lines 68 and 69, respectively.
2b and the upstream side of the flow meter 62 of the liquid supply line 61.

In the valve device 11, as shown in FIG. 2, before the liquid supply starts, both the electromagnetic valves 39 and 46 are de-energized and are in the upper switching position, respectively, and the lines 38 and 42 are cut off. Therefore, the liquid in the primary chamber 12b is introduced into the diaphragm chamber 12d via the lines 41, 40 (second communication path 43) and the liquid pressure is P ₁ =P ₃ , so the main valve body 14 is
The valve seat 1 is urged downward by the hydraulic pressure difference of P ₃ (=P ₁ ) - P ₂ acting on this and the urging force of the spring 16.
2a, and the main valve 17 is closed. Furthermore, since the main valve shaft 15 is at its lower limit of movement, the poppet 19 is also at its lower limit of movement, and the regulating valve 34 is fully open. Also, at this time, in the constant flow control valve 63, the lines 68 and 69
The hydraulic pressures in the upper chamber 63a and lower chamber 63b are the same, and the diaphragm membrane 65 is pressed downward by the spring 64 and is at its lower limit of movement, and the control valve portion 67 is fully open (see Fig. 2). indicates the fully open state of the control valve section 67).

Next, the operation of the valve device 11 will be explained.
At the start of liquid supply, the electromagnetic valve 39 is first energized and slides downward in FIG. 2 to bring the piping line 38 into communication. Then, the diaphragm chamber 12d
Since the liquid pressure P ₃ of the liquid is higher than the liquid pressure P ₂ (approximately atmospheric pressure) in the secondary chamber 12c, the flow path 25 of the outer cylinder 25
b, regulating valve 34, flow path 31a, and further line 38
It begins to flow out to the secondary chamber 12c side through. At this time, the liquid on the primary chamber 12b side flows into the diaphragm chamber 12d via the lines 41 and 40 (second communication path), but the inflow amount is throttled by the throttle 44, so it is small compared to the outflow amount. . Therefore, the amount of liquid in the diaphragm chamber 12d gradually decreases, and the liquid pressure increases.
The value of P ₃ becomes smaller.

Therefore, the main valve body 14 starts to move upward due to the hydraulic pressure _P1 acting on the diaphragm membrane 22, and the poppet 19
It is close to the valve seat 31b. Therefore, the opening degree of the regulating valve 34 becomes smaller, and the amount of outflow from the diaphragm chamber 12d gradually becomes smaller, and becomes the same as the amount of inflow from the line 40 when the main valve body 14 moves upward to a predetermined position. Therefore, at this time, the diaphragm chamber 12
Since the liquid amount d is balanced at a constant level, the main valve body 14 is also stopped at the above-mentioned predetermined position during upward movement and is balanced at that position.

In this way, the main valve 17 is balanced in a one-step open (half-open) state, and the liquid in the primary chamber 12b begins to steadily flow toward the secondary chamber 12c via the main valve 17, and liquid supply is started.

Next, after a predetermined period of time has elapsed since the start of the liquid supply, the electromagnetic valve 46 is energized and slid downward in FIG. 2 to bring the line 42 into communication. Then, the diaphragm chamber 12d is connected to the secondary chamber 1 via the lines 40 and 42 (third communication path) in addition to the line 38.
It will be in communication with 2c. However, since the liquid pressure _P3 of the liquid in the diaphragm chamber 12d is greater than the liquid pressure _P2 in the secondary chamber 12c (the liquid pressure in the secondary chamber 12c is
Since the main valve 17 is in a half-open state, the hydraulic pressure value of _P2 is still small), and begins to flow out to the secondary chamber 12c via the lines 40 and 42. Therefore, the diaphragm chamber 12d
The liquid amount decreases further, and the liquid pressure _P3 also becomes smaller.

Therefore, the main valve body 14 starts to move upward again from the above mid-movement position, the poppet 19 comes into contact with the valve seat 31b, the regulating valve 34 is closed, and the diaphragm chamber 12d
The flow of liquid through line 38 is eliminated.
The main valve body 14 further moves upward, and for example, the diaphragm retainer 23 comes into contact with the lower end of the outer cylinder 25 and stops (during this time, the poppet 19 compresses the spring 20 and
4), the main valve 17 is in a two-stage open (fully open) state. Thus, the liquid in the primary chamber 12b flows through the main valve 1.
A large amount of liquid begins to steadily flow to the secondary chamber 12c via the liquid supply port 7, and the liquid supply continues.

Next, at the end of liquid supply, the solenoid valve 46 is first de-energized and switched back to the solid line position in FIG.
Line 42 is cut off. Then diaphragm chamber 1
2d, both lines 38 and 42 in the outflow direction are closed, and the liquid from the primary chamber 12b side is gradually flowed in through the lines 41 and 40 (restriction 44), and the amount of liquid increases and the liquid pressure P ₃ also increases. . As a result, the main valve body 14 starts moving downward, and at the same time, the poppet 19 also moves toward the shaft 1.
8, and eventually returns to contact with the retaining ring 21. From this point onwards, the main valve body 1
4 moves downward, the poppet 19 separates from the valve seat 31b, the regulating valve 34 opens, and the diaphragm chamber 1
The liquid in 2d begins to flow out via the regulating valve 34 and line 38 again.

When the main valve body 14 moves further down and the outflow amount gradually increases until it becomes the same as the inflow amount from the lines 41 and 40, the amount of liquid in the diaphragm chamber 12d is balanced at a constant level, and the main valve body 14 It stops at a predetermined position during the downward movement. As a result, the main valve 17 is balanced in a one-stage closed (half-closed) state (same as the one-stage open state), and the flow of liquid through the main valve 17 is throttled.

Next, the electromagnetic valve 39 is de-energized and the line 39 is cut off as shown in FIG. Then, the diaphragm chamber 12d again connects both lines 3 in the outflow direction.
Both lines 8 and 42 are closed, and lines 41 and 40 are still closed.
The liquid is flowed into the diaphragm chamber 12d through the diaphragm chamber 12d.
The hydraulic pressure _P3 increases, the main valve body 14 starts moving downward again and seats on the main valve seat 12a, and the main valve 17 is closed in two stages (fully closed).

By varying the screwing amount of the guide 31, the one-stage open (or one-stage closed) position of the main valve body 14 can be variably set, and as in the past, changing this position required replacing the auxiliary valve. It's less troublesome compared to.

According to the above configuration and operation, the main valve 17 is the only valve through which the supply liquid passes, and the low flow adjuster 24 (adjusting valve 34) and two electromagnetic valves 39 and 46 are simply provided for controlling the hydraulic pressure. There is no need for an auxiliary valve, manifold, or complicated piping for passing the supply liquid, and the configuration and operation can be greatly simplified.

Next, constant flow control by the pilot constant flow control valve 63 when the main valve 17 is fully open (two-stage open) will be explained. Due to the original characteristics of the flow meter 62, when a constant flow of liquid flows, the differential pressure before and after the flow becomes a fixed predetermined value, and as the liquid flow rate becomes larger than the constant flow rate, the differential pressure value increases, and conversely, it decreases. The above differential pressure value becomes smaller as the value increases.

Therefore, a preset constant flow rate of liquid flows through the main valve 17.
When the fluid is flowing under the fully open condition, the hydraulic pressure (P ₅ ) in the lower chamber 63b of the control valve 63 changes to the upper chamber 63a via the lines 68 and 69 based on the predetermined pressure difference.
(P ₅ > P ₄ ) compared to the hydraulic pressure (P ₄ ). Therefore, the diaphragm membrane 65 moves slightly above the lower limit of movement, and the control valve section 67 is balanced at a predetermined valve opening degree that is slightly closed compared to the fully open state when no liquid flows into the supply line 61.

Here, when the liquid flow rate becomes larger than the above-mentioned set flow rate and the above-mentioned differential pressure (P ₅ to _{P 4} ) becomes larger than the predetermined value,
The diaphragm membrane 65 and the valve body 66 move further up from the above-mentioned balanced state, and the valve opening degree of the control valve section 67 becomes smaller than the above-mentioned predetermined valve opening degree. Therefore, since the amount of liquid flowing out to the secondary chamber 12c via the line 42 is small, the second communication path 43 (lines 40, 4
1), the amount of liquid flowing into the diaphragm chamber 12d increases, the hydraulic pressure _P3 increases, and the main valve body 14 moves downward somewhat to balance. Therefore, the opening degree of the main valve 17 becomes small, and the large liquid flow rate decreases to return to the set flow rate.

Next, when the liquid flow rate becomes smaller than the set flow rate and the differential pressure (P ₅ - P ₄ ) becomes smaller than the predetermined value, contrary to the above case, the valve opening of the control valve section 67 changes. Becomes large. Therefore, the liquid in the diaphragm chamber 12d flows out to the secondary chamber 12c via the third communication path 45, and the liquid pressure _P3 decreases. Therefore, the opening degree of the main valve 17 increases, and the small liquid flow rate increases and returns to the set amount.

According to the configuration of the control valve 63 described above, since the control valve 63 is independent from the main valve 17, the configuration and operation are simple, and if the control valve 63 is removed from the line 42, the main valve 17 can be easily replaced. It can be used as a step-opening/closing metering valve, improving usability.

The valve device 11 controls the flow meter 6 by means of a control valve 63.
2 directly detects the differential pressure before and after 2 to keep the differential pressure value constant, but then the hydraulic pressure in the secondary chamber 12c of the main valve 17 is detected and indirectly keeps the differential pressure value constant. Fig. 4 shows what is maintained, and the same parts as in Fig. 2 are given the same reference numerals.

In FIG. 4, in the valve device 71, a control valve 63' is interposed in the line 42, and the lower chamber 63b is communicated with the secondary chamber 12c via the line 72.

According to this, when the liquid flow rate becomes larger than the set flow rate, the liquid (P ₂ ) in the secondary chamber 12c increases,
This is introduced as pilot pressure into the lower chamber 63b of the control valve 63' via the line 72, pushing up the diaphragm membrane 65. Therefore, similarly to the above case, the valve opening degree of the control valve section 67 becomes small, and the main valve 17
The valve opening becomes small and the liquid flow rate decreases to return to the set flow rate.

Next, when the liquid flow rate becomes smaller than the set flow rate, the liquid pressure (P ₂ ) in the secondary chamber 12c becomes small, and this is introduced into the lower chamber 63b of the control valve 63', so the diaphragm membrane 65 moves downward. . Therefore, the control valve section 67
The valve opening of the main valve 17 becomes large, and the liquid flow rate increases to return to the set flow rate.
According to this, the liquid flow rate is always constant, so
Conversely, it is guaranteed that the differential pressure before and after the flow meter 62 is also at a predetermined value, and the flow rate measurement by the flow meter 62 is also performed normally.

As described above, the valve device according to the present invention is applied to both the fixed-rate valve and constant-flow valve functions of the liquid supply line to a lorry vehicle, and the main valve is the only valve through which the liquid to be supplied passes. Since the main valve is controlled in two stages by simply providing a regulating valve for controlling hydraulic pressure and two communication passage opening/closing means, there is no need for auxiliary valves, manifolds, etc., simplifying the overall configuration and operation, and reducing costs. Moreover, since the pilot type constant flow control valve is installed separately from the main valve body and in the middle of the communication path, the control valve is independent and does not need to be mechanically linked with the main valve. It is easy to operate, has a simple structure, and is convenient in use when used simply as a metering valve, without requiring a replacement lid or the like, and simply removing the control valve.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a conventional example of a valve device, FIG. 2 is a vertical cross-sectional view of an embodiment of the valve device according to the present invention, and FIG.
The figure is an enlarged vertical cross-sectional view of the main part thereof, and FIG. 4 is a vertical cross-sectional view of another embodiment of the above-mentioned valve device. 1, 11, 71... Valve device, 2... Valve body, 3, 1
4... Main valve body, 5, 17... Main valve, 6... Auxiliary valve body, 8
...Auxiliary valve, 9...Manifold, 12b...Primary chamber,
12c...Secondary chamber, 12d...Diaphragm chamber, 15
...Main valve shaft, 19...Poppet, 22, 53, 65...
Diaphragm membrane, 24...Low flow adjuster,
31...Guide rod, 34...Adjusting valve, 38...First communication path (piping line), 40, 41, 42, 68,
69, 72... Piping line, 39, 46... Solenoid valve,
43...Second communication path, 45...Third communication path, 5
2, 63, 63'... Pilot type constant flow control valve,
54... Plunger, 55... Small valve, 57, 62... Flow meter, 67... Control valve section.

Claims (1)

[Scope of Claims] 1. A main valve including a first valve seat and a first valve body that can move toward and away from the valve body disposed in a liquid supply line, and a primary chamber of the main valve. a diaphragm membrane fixed between the valve body and the first valve body and defining a diaphragm chamber; a first communication passage communicating the diaphragm chamber with the secondary side of the main valve; a second valve seat arranged in the middle of the communication path of the first valve; and a second valve seat that faces the second valve seat and is displaced integrally with the first valve body.
an adjusting valve comprising a second valve body that seats on the second valve seat when the valve body moves a predetermined amount in the valve opening direction;
A first communication passage opening/closing means arranged in the middle of the first communication passage, a second communication passage communicating between the primary side of the main valve and the diaphragm chamber, and a secondary side of the diaphragm chamber and the main valve. a third communication path communicating between the two, a throttle disposed midway through the second communication path, a second communication path opening/closing means disposed midway through the third communication path, and a third communication path The fluid pressure at a predetermined point in the fluid supply line is introduced as a pilot pressure, and the valve opening of the control valve section is made variable to control the flow rate in the third communicating path. 1. A valve device comprising a pilot type constant flow control valve that maintains a constant flow rate in a liquid supply line. 2. The liquid pressure at a predetermined point in the liquid supply line is the differential pressure between the liquid pressures on the liquid inflow side and the liquid outflow side of a flow meter provided upstream of the valve body of the supply line. A valve device according to claim 1. 3. The valve device according to claim 1, wherein the hydraulic pressure at a predetermined portion of the liquid supply line is the hydraulic pressure on the secondary side of the supply line.