Pressure Regulator Details (III) : How to Use a Pressure Regulator Flow Chart



Basic Knowledge



Principle and application of pressure regulators

The pressure regulators adopt a special flow path structure (as shown in Figure 1). 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).

Fload element = Fsensing element + Fcontrol element Formula (1)


Fload element = range spring load

Fsensing element = outlet pressure × diaphragm effective area

Fcontrol element = inlet pressure × poppet effective area + poppet spring load

Figure 1 Structure Diagram of Pressure Regulators

Figure 1 Structure Diagram of Pressure Regulators

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 (shown in Figure 2) describes the relationship between flow rate (horizontal axis) and outlet pressure (vertical axis) 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 range of system pressures that a pressure regulator can maintain at given flow rates.

Figure 2 Flow Chart Diagram of Pressure Regulators

Figure 2 Flow Chart of Pressure Regulators

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

How to Use a Flow Chart?



Flow chart analysis

Valve manufacturers usually provide multiple flow curves for the same series of regulator 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 flow rate, the vertical axis represents the outlet pressure value, and the inlet pressure is represented by curves of different colors, such as 3000 psig (206.8 bar), 2000 psig (137.9 bar) and 1000 psig (68.9 bar). When the 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 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 of that point from vertical axis. If the flow curve for the required pressure condition can't be found in the pressure regulator flow chart provided, a new curve can be deduced 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 70℉ (20°C). If the actual system uses other medium 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 FG X FT Formula (2)

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

Table 1

Medium Type
Gravity Modified Coefficient ( FG )



Carbon dioxide



Hydrogen chloride








Ammonia gas







Table 2

Temperature ( °F )
Temperature( °C )
Temperature Modified Coefficient ( FT )






































Application Examples



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), etc., 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.

FITOK Pressure Regulator Products

Figure 3 FITOK Pressure Regulator Products

Selection example

For example, the flow chart for FITOK FCR-1S series pressure regulators is shown in Figure 4. The customer requires to determine the outlet pressure when the inlet pressure is 3000 psig (206.8 bar), the outlet set pressure is 90 psig (6.2 bar), the operating temperature is 100°F (37°C), and the system medium (CO2) flow rate is 10 SCFM (283 SLPM)

FCR-1S Series Pressure Regulators

Figure 4 Flow Chart of FCR-1S Series Pressure Regulators

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 by the manufacturer, the flow rate scale shall be modified according to the gravity modified coefficient (FG) and temperature modified coefficient (FT). As can be seen from Table 1, when the medium is carbon dioxide, the corresponding gravity modified coefficient FG is 0.80. And from Table 2, when the temperature is 100°F (37°C), the corresponding temperature modified coefficient FT is 0.97. Bring the initial flow rate scale (i.e. the horizontal axis value) in Figure 4 and FG and FT into formula (2), calculate to get the modified flow rate scale (example: 3.9 = 5 x 0.8 x 0.97). Replace the horizontal axis in Figure 4 with the modified flow rate scale while keeping the vertical axis and flow curve the same to get a new flow chart as shown in Figure 5.

Regulators after Modification

Figure 5 Flow Chart of Pressure Regulators after Modification

As can be seen in Figure 5, the flow curve for the customer's desired inlet pressure of 3000 psig (206.8 bar) and outlet set pressure of 90 psig (6.2 bar) is not shown. We can interpolate and analogize according to the two flow curves for an inlet pressure of 3000 psig (26.8 bar) and outlet set pressures of 75 psig (5.2 bar) and 100 psig (6.9 bar) to get a flow curve for the inlet pressure of 3000 psig (206.8 bar) and outlet set pressure of 90 psig (6.2 bar) as shown in the red curve in Figure 6.

Interpolation and Analogy

Figure 6 Flow Chart after Interpolation and Analogy

From the flow curve (red curve) shown in Figure 6 for the inlet pressure of 3000 psig (26.8 bar) and outlet set pressure of 90 psig (6.2 bar), find the point A on the curve with horizontal axis scale of 10 SCFM (283 SLPM), and get the actual outlet pressure of 84 psig (5.8 bar) from vertical axis.

Therefore, for FCR-1S series pressure regulators at the inlet pressure of 3000 psig (206.8 bar), the outlet set pressure of 90 psig (6.2 bar), the operating temperature of 100°F (37°C) and the system medium (CO2) flow rate of 10 SCFM (283 SLPM), the actual outlet pressure is 84 psig (5.8 bar).




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.


Related Articles:

This website uses cookies in order to improve your user experience. By clicking "Accept" or continuing to use our website, you consent to our use of cookies as defined in this Cookie Policy. Cookie Notice and Disclosure

Last updated June 16, 2020


Like many companies, FITOK Group, its subsidiaries and its authorized sales and service centers (collectively, "FITOK" or "we, " "us, " or "our") use "cookies" and similar tools on and any authorized sales and service center website (collectively, the "Sites") to facilitate and improve your online experience. This Notice explains how we do that.  
What are cookies?
A cookie is a small file or piece of information which is downloaded to your computer or device when you visit the Sites, and then sent back to the Sites in order to allow us to recognize your computer or device later. Although certain cookies may contain personal data – for example, if you click to "remember me" when logging in, a cookie may store your username – most cookies won’t collect personal data that identifies you. Rather, most cookies collect general information, such as how users arrive at and use the Sites, or a user’s general location. By collecting this information, cookies help to analyze web traffic and allow web applications to respond to you as an individual. The web application can tailor its operations to your needs, likes and dislikes by gathering and remembering information about your preferences.
How do we use cookies?
Our Sites utilize cookies for several purposes, including the storage of information required to determine how to properly deliver content to your computer or device. A cookie is provided to all visitors to, regardless of whether you register with an authorized sales and service center.
For users who do register with an authorized sales and service center, a profile containing the registration information is generated by our website, and used for several purposes:
  1. to match you with content that is associated with your interests and to direct you to additional resources and tools that can save you time;
  2. to enable a fast response for service or follow-up request from our website;
  3. to verify your identity;
  4. to send you an electronic newsletter, other information and content; and
  5. to contact you when necessary.
What kinds of cookies do we use?
We may use cookies for a number of purposes:
  1. Session Cookies These cookies are used 'in-session' each time you visit and then expire when you leave a Site or shortly thereafter.  They are not stored on your computer or device permanently, do not contain any personal data and help by minimizing the need to transfer personal data across the internet. These cookies can be deleted or you can refuse to allow their use, but this will hamper the performance and your experience in using the Sites. These cookies also take time stamps that record when you access the Sites and when you leave the Sites.
  2. Tracking Cookies – These cookies enable us to recognize repeat visitors to the Sites. By matching an anonymous, randomly generated identifier, a tracking cookie keeps track of where a user of the Sites came from, what search engine they may have used, what link they clicked on, what keyword they used and where they were in the world when they accessed the Sites. By monitoring this data, we can make improvements to the Sites.
  3. Persistent Cookies – This type of cookie is saved on your computer or device for a fixed period (sometimes for a few hours, sometimes for a year or longer) and is not deleted when the browser is closed. Persistent cookies are used where we need to remember who you are for more than one browsing session. For example, this type of cookie can be used to store your preferences, so that they are remembered for the next visit to the Sites.
  4. Performance or Analytical Cookies Performance cookies are used to analyze how the Sites are used and to monitor their performance, which allows us to improve your experience in using the Sites. These cookies help us to tailor the content of the Sites to reflect what the Site users find most interesting and to identify when technical issues with the Sites arise. We may also use this data to compile reports to help us to analyze how Sites are used, what the most common issues are and how we can improve the Sites.
Can the Cookies be blocked?
Yes. Most internet browsers are initially set up to automatically accept cookies. You can, however, change your browser settings to block cookies or to alert you when cookies are being sent to your device. There are a number of ways to manage cookies. Please refer to your browser instructions or help screen to learn more about how to adjust or modify your browser settings. Instructions for blocking or allowing cookies in popular web browsing software can be found by clicking the following links:
Internet Explorer
Google Chrome
Microsoft Edge
Please be aware that if you disable the cookies that we use, this may impact your experience while on the Sites. For example, some features and services on the Sites may not work properly because we may not be able to recognize and associate you with your FITOK account(s). In addition, the offers we provide when you visit us may not be as relevant to you or tailored to your interests.