Principle and Application of Pressure Regulators

The pressure regulators adopt a special flow path structure. When the high pressure medium flows through the orifice from the inlet, the flow rate of the medium increases and the pressure decreases, thus achieving the purpose of pressure regulation. In addition, the pressure regulators can balance the medium load generated by the inlet pressure and the outlet pressure by adjusting the spring load, so as to control the outlet pressure and maintain it, and the force balance of the pressure regulators meets the formula (1).

F_{load element} = F_{sensing element} + F_{control element} Formula (1)

Where:

F_{load element} = range spring load

F_{sensing element} = outlet pressure × diaphragm effective area

F_{control element} = inlet pressure × poppet effective area + poppet spring load

The main purpose of the pressure regulators is to reduce the upstream inlet pressure to the set outlet pressure value and maintain it, so as to meet the specific system pressure requirements. Pressure regulators are widely used in the fields of special gas, high purity and the like.

Composition and function of a flow chart

The flow chart describes the relationship between flow rate and outlet pressure of the pressure regulators at a given inlet pressure. From this chart, we can see the response state of the pressure regulators when the flow rate in the system changes. It describes the system pressures range that a pressure regulator can maintain at a given flow rate.

From the flow chart, we can judge whether the selected pressure regulators meet the requirements of actual system working conditions, thus contributing to rapid part number selection.

Flow Chart Analysis

Valve manufactures usually provide multiple flow curves for the same series of regulators at different inlet pressures and the same outlet pressure to illustrate the operating range of the regulator. As shown in figure 2, the horizontal axis represents the medium flow rate, the vertical axis represents the outlet pressure valve, and the inlet pressure is represented by curves of different colours. When the medium flow rate is 0, the outlet pressure shown in the vertical axis is the outlet set pressure.

The flow curve shows a ‘droop’ trend, that is, under a certain inlet pressure and outlet set pressure conditions, with the medium flow rate gradually increases, the outlet pressure gradually decreases. As the internal structure and component limit, pressure regulators cannot provide a perfect horizontal flow curve in a particular regulating state. As a consequence, when the pressure regulators respond to the increase of flow rate, the outlet pressure will decrease to some extent.

For pressure regulator application, it is usually required to maintain a relatively constant outlet pressure when the system flow changes greatly. Therefore, the less droop of the flow curve, the better performance of the pressure regulator.

How to Use a Flow Chart

For a certain type of pressure regulator, first find the corresponding flow chart, and select the corresponding curve according to the actual inlet pressure and outlet set pressure values. Then find its corresponding point on the curve according to the horizontal axis flow rate scale and get the actual outlet pressure value of that point from vertical axis. If the flow curve for the required pressure condition cant be found in the pressure regulator flow chart provided, a new curve can be deducted between two adjacent existing curves.

In addition, the flow chart provided by the manufacturer is based on test conditions when the test medium is nitrogen and the test temperature is 20°C. If the actual system uses other media and at other operating temperature, the flow rate scale in the horizontal axis of the flow chart needs to be modified according to formula (2), and the curve trend remains unchanged.

Q₂ = Q₁ X F_G X F_T Formula (2)

In the formula, Q₁ is the initial flow scale, Q₂ is the modified flow rate scale, F_G is the gravity modified coefficient, F_T is the temperature modified coefficient. The values of F_G and F_T can be referred to in Table 1 and Table 2 respectively.

Table 1

Media Type	Gravity Modified Coefficient ( FG )
Arsine	0.60
Carbon Dioxide	0.80
Argon	0.84
Hydrogen Chloride	0.87
Silane	0.93
Oxygen	0.94
Air	0.98
Ammonia Gas	1.28
Helium	2.65
Hydrogen	3.72

Table 2

Temperature (℉)	Temperature (℃)	Temperature Modified Coefficient ( FT )
-40	-40	1.12
-20	-28	1.10
0	-17	1.07
20	-6	1.05
70	20	1.00
100	37	0.97
150	65	0.93
212	100	0.89
250	121	0.86
300	148	0.84
350	176	0.81
400	204	0.78

FITOK Pressure Regulator Products

The FITOK pressure regulator products include: cylinder pressure regulators (FCR-1, FCR-1S, FCR-1D series, etc), line pressure regulators (FLR-1, FBR-1, HPR-10 series, etc), changeover systems (FDR-1, CEPR, DPPR series etc), high purity pressure regulators (FHR-1 series), are suitable for cylinder pressure regulation, pipeline system pressure regulation, pressure control and changeover conditions thus widely used in special gas, high purity and other fields.

For example, the flow chart for FITOK FCR-1S series pressure regulators shown in figure 4. The customer requires to determine the outlet pressure when the inlet pressure is 206.8 bar, the operating temperature is 37°C, and the system medium flow rate is 10 SCFM.

Since the medium type and operating temperature required by the customer are inconsistent with the test medium and test temperature of the flow chart provided the manufacturer, the flow rate scale shall be modified according to the gravity modified coefficient and temperature modified coefficient. When the medium is carbon dioxide, the corresponding gravity modified coefficient is 0.80 and when the temperature is 37°C, the corresponding temperature modified is 0.97.

As can be seen in figure 5, the flow curve for the customers desired inlet pressure of 3000 psig and outlet set pressure of 90 psig is not shown. We can interpolate and analogize according to the two flow curves for an inlet pressure of 3000 psig and outlet set pressures of 75 psig and 100 psig to get a flow curve for the inlet pressure of 3000 psig and outlet set pressure of 90 psig as shown in the red curve in figure 6.

From the flow curve shown in figure 6 for the inlet pressure of 3000 psig and outlet set pressure of 90 psig, find the point A on the curve with horizontal axis value of 10 SCFM, and get the actual outlet pressure of 84 psig from vertical axis. Therefore, for FCR-1S series pressure regulators at the inlet pressure of 3000 psig, the outlet set pressure of 90 psig, the operating temperature of 37°C and the system medium flow rate of 10 SCFM, the actual outlet pressure is 84 psig.

Conclusion

By correctly using the flow chart of the pressure regulators, we can verify whether the working pressure range of the selected type of pressure regulators meets the customer’s requirements, thus contributing to rapid and accurate part number selection. In addition, the flow chart can also reflect pressure regulators’ pressure regulating performance.

For more information contact our sales team at sales@nvfcl.com or 01942601209