FORM 2
THE PATENTS ACT. 1970 (39 of 1970)
COMPLETE SPECIFICATION (Section 10, rule 13)
A PILOT OPERATED GAS PRESSURE REGULATOR CONFIGURED TO FAIL
CLOSE
Chemtrols Industries Limited
an Indian Company registered under the provisions of the Companies Act, 1956, with our Corporate office at Amar Hill, Mumbai 400 072., Maharashtra, India.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

FIELD OF INVENTION
The present invention relates to a pilot operated gas pressure regulator configured to fail close.
BACKGROUND
Pressure regulators are devices designed to monitor and control the amount of pressure running through a system of some type. Regulators are used to allow high-pressure fluid supply lines or tanks to be reduced to safe and/or usable pressures for various applications. A pressure regulator must supply a quantity of flow that matches a downstream, usage, demand. If the required flow rate is small, the regulator plug or disk should approach its seat and restrict the flow. When the demand increases, the plug or disk should move away to create a larger opening. Ideally, a regulator should provide a constant downstream pressure while delivering the required flow. Therefore, regulators automatically adjust the flow rate to meet the downstream demand. Typically, gas pressure regulators are of two categories:
a) Self-Operated/ Direct-Operated Pressure Regulator; and
b) Pilot-Operated Pressure Regulator.
a) Self-Operated/ Direct-Operated Pressure Regulator: Direct-operated regulators have three essential elements:
i) Restricting Element: The regulator's restricting element is generally a disk or plug that can be positioned fully open, fully closed, or somewhere in between to control the amount of flow. When fully closed, the disk or plug seats tightly against the valve orifice or seat ring to shutofif flow.
ii) Measuring Element: The measuring element is usually a flexible diaphragm that senses downstream pressure as pressure beneath it changes. The restricting element is often attached to the diaphragm with a stem so that when the diaphragm moves, so does the restricting element. iii) Loading Element: A weight or spring acts as the loading element. The loading element counterbalances downstream pressure unbalance between the loading element and the measuring element determines the position of the restricting element. Therefore, we can adjust the desired

amount of flow through the regulator, or set point, by varying the load. Some of the first direct-operated regulators used weights as loading elements. Most modern regulators use springs.
An example of a self-operated regulator is a spring-opened valve directly opposed by a diaphragm assembly at increasing downstream pressure, acts on the diaphragm assembly to overcome the force of the spring, closing the valve. When downstream pressure falls, spring force is greater than the force of the gas acting on the diaphragm and the valve opens. In all type of regulator valves, a control inaccuracy caused is by "droop" or "offset". Offset effect occurs ' as the demand for gas in the downstream system increases. When the regulator is required to pass more gas to the downstream system, the regulator valve plug must be opened to allow more flow. To allow this opening of the valve plug, the downstream pressure sensed by the diaphragm must decrease. By allowing the downstream pressure, to decrease, less force opposes the compressed spring and the valve plug is pushed farther open to meet the flow demand of the system. The net effect is a decrease or offset of downstream control pressure from the desired set pressure.
b) Pilot-Operated Pressure Regulator: In the evolution of pressure regulator designs, the shortcomings of the direct-operated regulator naturally led to attempts to improve accuracy and capacity. A logical next step in regulator design is to use what we know about regulator operation to explore a method of increasing sensitivity that will improve all of the performance criteria.
To improve the sensitivity of the regulator, a downstream pressure is to be sensed and then somehow make a change in loading pressure that is greater than the change in downstream pressure. To accomplish this, a device called a pilot can be used. The major function of the pilot is to increase regulator sensitivity. If we can sense a change in downstream pressure and translate it into a larger change so that the regulator will be more responsive (sensitive) to changes in demand. In addition, droop can be significantly reduced so its effect on accuracy and capacity is minimized.

OBJECTIVES
An object of the present invention is to regulate the gas pressure with maximum possible
accuracy.
SUMMARY OF THE INVENTION
Present invention introduces a device for regulating gas pressure in a pipe or duct carrying high pressure gas. The pilot operated gas pressure regulators are commonly used in high pressure natural gas pipelines. The present device comprises a control valve with an inlet chamber connected to the high pressure gas duct, an outlet chamber connected to the low pressure gas delivery line, and an intermediate path connecting the inlet chamber and the outlet chamber. The intermediate path has a regulating shutter or closure element which opens or closes the path. The control valve further comprises of integral actuator comprising a lower chamber and an upper chamber, having a compression spring located in each chamber and separated by a flexible diaphragm having a compression spring located at upper side and lower side of it; the diaphragm is attached to the closure element with a rigid rod; and is adapted for closing or opening the closure element. These compression-springs help in regulating the shutter and the valve so as to maintain the flow rate of the gas depending upon the consumption of the gas by the users thereby keeping the system in a state of dynamic balance. The device is responsible for closing the regulating shutter in case of any failure in the actuating system or power source for actuation. Such a regulator is generally referred to as a regulator configured to Fail Close. By doing so it prevents the high pressure gas from the inlet stream to pass to the delivery line without regulation.

BRIEF DESCRIPTION
Figure 1 illustrates a schematic of a pilot operated gas pressure regulator of present invention.
DETAILED DESCRIPTION OF THE INVENTION
Present invention introduces a device for regulating gas pressure in a pipe or duct carrying high pressure gas. The pilot operated gas pressure regulators are commonly used in high pressure natural gas pipelines. Natural gas is transported through pipelines under high pressures to minimize the cost and for convenience. At the point of use the pressure required is much lesser than the high pressures at which it is transported. This pressure reduction is achieved through pressure regulators at different stages. The flow rate of the gas depends on the consumption of the gas by the end users and a constant supply pressure is maintained by a regulating valve which responds dynamically to these changes in the flow rates.
The device of present invention comprises a control valve with an inlet chamber connected to the high pressure gas duct (1), an outlet chamber connected to the low pressure gas delivery line (2), and an intermediate path connecting the inlet chamber and the outlet chamber.
With reference to figure of the invention, the intermediate path has a regulating shutter (3) or closure element which opens or closes the path. The control valve further comprises of integral actuator comprising an upper chamber and a lower chamber separated by a flexible diaphragm which is attached to the closure element with a rigid rod; and is adapted for closing or opening the closure element.
According to an embodiment of the present invention, a first compression spring (8) is located on the upper side of the diaphragm, which exerts a downward force to the regulating shutter and moves it down to close the valve. The upper chamber of the actuator is connected to the low pressure delivery line so that the pressure inside the upper chamber is same as that of the delivery line. The motorisation pressure is supplied from the pilot (9) to the lower chamber of the

actuator. The net force acting against the force due to the differential pressure across the diaphragm is the resultant of spring force, the weight of the moving parts and the various frictional forces on the moving parts. The pilot senses the pressure in the delivery line and compares it with the desired pressure and gives the motorizing pressure accordingly. When the sensed pressure is less than the set pressure, the pilot supplies the motorisation pressure to the lower chamber of the actuator. In this case, the motorisation pressure is more than the sensed pressure so that there will be a net upward force to move the regulating shutter upwards or to open the regulator. When the sensed pressure is equal to the set pressure, the net force acting upwards equals the net force acting downwards and the regulating shutter remains stationary. When the sensed pressure is more than the set pressure, the supply of motorisation pressure is stopped from the pilot, thereby the pressure in the upper and lower chambers of the actuator equalises since both the chambers are connected through a bleed hole. When there is no net differential pressure across the diaphragm the spring force will tend to close the regulating shuner so that the delivery pressure reduces.
The performance of a regulator is assessed by its ability to maintain a constant pressure in the gas delivery line over a large range of operation of the valve, and by thevariation it tolerates in the desired set pressure. Hence the response of the regulator to a disturbance in the system must be adequately fast. So when there is a disturbance in the pressure in the delivery line, the motorisation pressure must be able to bring about the desired change at the earliest. When this desired change is to open the valve further, the motorization pressure shall take care in addition to the force required to further compress the spring, the force required to overcome the weight of the moving parts as well as the frictional forces. So for the regulator to respond it has to build the pressure inside the lower chamber of the actuator to a value sufficient enough to overcome the above mentioned forces. Inorder to overcome the above drawbacks, the device of the present* invention has a second compression spring (10) located on the bottom side of the diaphragm. Thus, the second compression spring is adapted for exerting a force sufficient enough to balance the weight of the moving parts and to overcome the frictional forces, thereby keeping the system in state of dynamic balance and helping in improving the performance of the regulator.

We claim,
1. A pilot operated device for regulating gas pressure; the device comprising a control valve with an inlet chamber connected to the high pressure gas duct, an outlet chamber connected to the low pressure gas delivery line, and an intermediate path connecting the inlet chamber and the outlet chamber and having a regulating shutter or closure element which opens or closes the path.
2. A device as claimed in claim 1, wherein the control valve further comprises of integral actuator comprising an upper chamber which being connected to the low pressure delivery line and a lower chamber separated by a flexible diaphragm which is attached to the closure element with a rigid rod; and is adapted for closing or opening the closure element.
3. A device as claimed in claim 1, wherein a pilot is meant for supplying motorization pressure to lower chamber of the actuator and further adapted for sensing the pressure in the delivery line and comparing it with the set pressure.
4. A device as claimed in claim 1, wherein the device has a first compression spring located on the upper side of the diaphragm exerting a downward force to the regulating shutter and • moves it down to close the valve.
5. A device as claimed in claim 1, wherein the motorisation pressure being supplied from the pilot to the lower chamber of the actuator; the pilot being adapted for sensing the pressure in the delivery line and comparing it with the set pressure.
6. A device as claimed in claim 1, wherein when the sensed pressure is less than the desired pressure, the motorisation pressure is supplied from the pilot to the lower chamber of the actuator; the motorisation pressure being more than the sensed pressure so that a*net upward force is exerted to move the regulating shutter upwards or to open the regulator.
7. A device as claimed in claim 1, wherein when the sensed pressure is same as that of the desired set pressure, the net force acting upwards is equal to the net force acting downwards and thus regulating shutter being remaining stationary.

8. A device as claimed in claim 1, wherein when the sensed pressure is more than the set pressure, the supply of the memorisation pressure is stopped from the pilot thereby the pressure in the upper chamber of the actuator is equal to the pressure in the lower chambers of the actuator.
9. A device as claimed in claim 1, wherein when no net differential pressure across the diaphragm, the spring force close the regulating shutter, resulting in decrease in the delivery pressure; the net force acting against the force due to the differential pressure across the diaphragm is the resultant of the spring force, the weight of the moving parts and the various frictional forces on the moving parts.
10. A device as claimed in claim 1, wherein the device further has a second compression spring located on the bottom side of the diaphragm. This second compression spring is adapted for exerting a force sufficient enough to balance the weight of the moving parts and to overcome the frictional forces, thereby keeping the system in state of dynamic balance and helping in improving the performance of the regulator.