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How a Self Operated Pressure Reducing Regulator Works

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A self operated pressure reducing regulator is a mechanical device that is used to control and reduce pressure especially in natural gas plants. A pressure regulator is essentially a force balanced device that adjusts to changes in the system it is controlling. There are two types of pressure reducing regulators used in natural gas systems:
1. Self operated regulators
2. Pilot operated regulators
Both types of regulators are very common in the gas industry the self-operated regulators are general used in lower flow and lower pressure system, and are less expensive regulators. While the pilot operated regulators are generally use in higher flow situation, like city gates, large customers, industrial accounts etc and where you have higher pressure to control.

Basic Parts of a Self Operated Pressure Reducing Regulators
Self Operated regulators consist of three basic components:
1. A loading element. 
2. A measuring element and 
3. A restrictive element as shown below

Self Operated Pressure Reducing Regulator

As seen above, the loading element is typically a spring but it can also be a weight or pressure from some external source. When the spring is compressed, it exerts a loading force. The measuring element or diaphragm is connected to the process fluid (gas) that is being controlled and creates a force opposing the loading force. The restricting element or valve is connected to the spring and diaphragm assembly and regulates the flow through the regulator.

Operating Principle of Self Operated Pressure Reducing Regulators
In a self operated pressure regulator, as downstream system pressure decreases the spring force overcomes the force of the gas acting on the effective area of the diaphragm and the valve opens increasing flow into the system. When system pressure increases, the measuring force (the force of the system gas acting on the effective area of the diaphragm) overcomes the loading force (spring force) and closes the valve reducing flow into the system.





What is Damping in Process Transmitters

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A process transmitter typically ”measures” a process variable – flow, level, temperature, pressure - and produces an output in response to changes in the input variable. Most transmitters incorporates a sensor which measures the input variable and gives out an output of which 4 – 20m A is common.



Of critical importance in the performance of a transmitter is a concept called damping. As the input variable changes, the transmitter output must update and change accordingly. Damping is the amount of time required, in addition to the update time, for the output of the transmitter to reach 63.2% of its final value after a step change has been applied to the input. A typical damping response curve of a process transmitter is shown below:


Transmitter damping is adjustable from 1 to 32 seconds. Damping reduces the effects of electrical noise and any other insignificant transient noise that may influence the transmitter output signal. It is often used to stabilize control loops and prevent false trips. In the absence of electrical or transient noise, damping may not be required in processes that are slow and have inherent lag time e.g temperature control loops. Damping should be minimized in fast changing process conditions.





ANSI B16.5 - Maximum Pressure and Temperature Ratings of Flanges and Flange Fittings

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The Maximum allowable non-shock pressure (psig) and temperature ratings for steel pipe flanges and flanged fittings according the American National Standard ANSI B16.5 are given in the table below. 

Flanges and their Fittings are a common feature in the process plants. The need to accurately determine their pressure rating and corresponding temperature ratings is important for personnel and plant safety and overall plant performance and reliability:


Maximum Allowable Non-Shock Pressure (Psig)
Temperature (°F)
Pressure Class (lb)
150
300
400
600
900
1500
2500
Hydrostatic Test Pressure (Psig)
450
1125
1500
2225
3350
5575
9275
-20 to 100
285
740
990
1480
2220
3705
6170
200
260
675
900
1350
2025
3375
5625
300
230
655
875
1315
1970
3280
5470
400
200
635
845
1270
1900
3170
5280
500
170
600
800
1200
1795
2995
4990
600
140
550
730
1095
1640
2735
4560
650
125
535
715
1075
1610
2685
4475
700
110
535
710
1065
1600
2665
4440
750
95
505
670
1010
1510
2520
4200
800
80
410
550
825
1235
2060
3430
850
65
270
355
535
805
1340
2230
900
50
170
230
345
515
860
1430
950
35
105
140
205
310
515
860
1000
20
50
70
105
155
260
430