Natural gas pressure regulators are designed to maintain outlet pressure at a constant
level independently of fluctuations in inlet pressure or gas flow. Under zero-flow
conditions, regulators close tightly.
Pressure regulators for natural gas can be found in several different design solution. For
situation where quick regulator response is used, like on gas trains and on other places
where sudden change of pressure is possible, direct acting pressure regulators are required.
Also, very common is use of
pilot operated pressure regulators, which you can read about
Direct acting pressure regulator is one that doesn't include pilot in its regulating circle.
These regulators are often having larger regulation error, in terms of RG, than pilot operated
pressure regulators. One possible construction is described bellow.
A system of levers transmits the movement of the spring loaded sensor and comparator
(diaphragm) to the control element. Pressure is regulated by changing the control variable
(control spring). The diameter of the outlet nozzle and of the duct connecting the sensor
and comparator is designed to produce a Venturi effect that overcomes the force of the
spring and causes outlet pressure to rise slightly as the flow of gas increases. At zero
gas pressure, the regulator is open, i.e. the controlling force (spring) presses down
on both the sensor and comparator and the lever system, so that the control element opens
and gas flows through the orifice. Outlet pressure then builds up and generates a force
exceeds the latter, the sensor raises the levers while the valve disk starts to close the
annular gap at the orifice, thus choking the gas flow and halting the outlet pressure build
up. As the outlet pressure downstream of the orifice goes down, bringing the diaphragm compartment
pressure down with it, the control element is opened by the force of the spring which now prevails.
This interaction is repeated until a balance has been achieved between the control force and the
outlet pressure acting on the comparator, which depends on the gas flow. If the control element
is damaged, or if the system of levers is jammed, any pressure buildup within the regulator
and downstream of the control element will be stopped as soon as the integrated safety
shutoff valve responds and cuts off the flow of gas.
Safety shut off valve function
Safety shut off valves will cut off automatically the flow of natural gas through a gas pressure
regulator as soon as gas pressure within the protected system reaches a specific upper response
As the outlet pressure increases, the diaphragm rises against the force of the control spring.
The connecting rod engages with the system of levers and releases the actuator and its
attached control element on which the force of the closing spring acts. The regulator is thus