The sizing and selection of Control Valves have considerations beyond the flow capacity (Cv) relating to conditions they will encounter in operation. These are divided into two main ratings: Body Pressure and Close-Off pressure.
Body Pressure Rating is a body and stem (shell) static rating, the amount of total pressure that the body and stem can contain without leaking. The body static pressure requirements for chilled and hot water valves are generally determined by the sum of the water column, fill, and pump pressures that the valve will experience. The pressure rating will be expressed in various ways depending on the valve manufacturer and type.
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System |
JIS Std |
DIN Std |
ASME Std |
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Sanitary |
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Marine |
JIS 5K |
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Water Work/
Fire Fighting |
JIS 10K |
PN10 |
Class 150 |
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PN16 |
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JIS 20K |
PN20 |
Class 300 |
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JIS 25K |
PN25 |
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Class 600 |
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Class 800 |
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Steam |
Class 900 |
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Class 1500 |
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Hight
Pressure |
Class 2500 |
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Class 4500 |
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Class 6000 |
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Cryogenic /
LNG/ LPG |
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Oil & Gas |
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Some valve manufacturers assign two ratings, fire rating and general service rating, to a valve. A UL-listed and FM-approved valve rated for 175 psig (1210 kPa) may have a general service rating of 400 psig (2760 kPa) at ambient temperature. It means that this valve can be used in a fire protection system having a maximum allowable working pressure of 175 psi (1210 kPa) or less, whereas it can be used in other services termed as general services and be subjected to a maximum allowable working pressure of 400 psig (2760 kPa).
the conversion rate is 1 psi = 0.0069mpa.
multiply the psi rating by 0.0069 and that will give you the mpa related to the
class
Dual or Multiple Ratings. A valve may be assigned one or more ratings by the valve manufacturer. Ratings assigned must be marked on the valve. The marking on the valve must be in accordance with the applicable valve standard or standards. A valve may comply with one or more valve standards. For example, a Class 600, NPS 4 (DN 100), butt-welding end, steel gate valve complying with ASME B16.34 may be marked as Class 800 valve in accordance with API Standard 603, provided the valve complies with the design and construction requirements of both ASME B16.34 and API 603. Some valve manufacturers may have proprietary design valves that are rated for specialty applications. Dual- or multiple-rated valves may be used within the pressure-temperature rating(s) conforming to the valve standard referenced in the code of jurisdiction under which the system is designed and constructed. Dual- or multiple-rated valves have increased utility and broad market. The manufacturer benefits from reduced design and production costs.
Pressure and temperature ratings take into account function and price to help customers easily select the most suitable valve for their work.
The pressure and temperature ratings refer to the relation between the fluid temperature and the maximum pressure each valve can withstand at that temperature. Products are grouped by material, and each is shown with its rating.
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Standard |
Designation |
Nominal pressure |
Remarks |
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JIS |
K |
5, 10, 16, 20, 30 |
Steel |
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(Japan) |
5, 7.5, 10, 16, 20 |
Cast iron : for 7.5 water pipe |
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5, 10, 16 |
Copper alloy |
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ASME |
Class |
75, 150, 300, 400, 600, 900, 1500, 2500,
4500 |
Steel |
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(USA) |
125, 250 |
Cast iron: for 7.5 water pipe |
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150, 300, 400, 600, 900, 1500, 2500 |
Copper alloy |
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DIN |
PN |
2.5, 6, 10, 16, 25, 40, 63, 100 |
Steel |
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(Germany) |
2.5, 6, 10, 16, 25 |
Cast iron: for 7.5 water pipe |
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BS |
Class |
150, 300, 400, 600, 900, 1500, 2500 |
Steel |
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(UK) |
PN |
2.5, 6, 10, 16, 25, 40 |
Steel, cast iron, copper alloy |
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Standard No. |
Title |
Outline |
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JIS |
B 2220 |
Steel pipe flanges |
1) |
Types |
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2) |
Relation between fluid temperature and maximum working pressure |
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3) |
Standard dimensions |
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4) |
Materials |
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Standard No. |
Title |
Outline |
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ASME |
B16.1 |
Cast iron pipe flanges |
1) |
Types |
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2) |
Pressure-Temperature Rating |
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3) |
Shape and dimensions |
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4) |
Materials |
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Common Ratings
WOG (Water, Oil, Gas) is a non-shock pressure rating for valves at ambient temperature. Oil refers to a free-flowing liquid containing higher viscosity than water and lubricating characteristics. Gas refers to a vaporized liquid, such as steam, and does not cover combustible gases. These will be expressed in PSI- 600 WOG equals 600 psi.
CWP (Cold Working Pressure) defines the maximum pressure rating for valves between -20F – 100F. These will be expressed in PSI- 200 CWP equals 200 psi.
PN (Pressure Nominal) is indicated in bar; for example, PN25 is 25 bar. 1 bar equals 14.5 psi. Sometimes manufacturers will include the psi rating as well.
Flanged or lug-style valves are categorized by ANSI flange classes covered under ASME B16 standards. Class 125 and 250 cover cast iron valves and flanges (B16.1). Class 150 and 300 covers ductile iron (B16.42), steel and stainless steel (B16.5). These ANSI classes have temperature pressure charts that correlate to the flange and/or valve ratings. Valves may indicate specific body pressure ratings exclusive of the flange rating.
Close-Off is the maximum differential across the ball or disc that the valve can hold against the rated seat leakage. The rated close-off pressure considers the entire assembly of the valve, actuator, and linkage. This pressure must be higher than the maximum differential pressure (Dp) the valve will be subjected to in the installation. The calculation is determined by the maximum pump differential for a two-way application. Valve close-off rating and maximum differential pressure rating may differ due to valve trim limitations. For example, a CCV may have a 200 psi close-off rating but a maximum Dp rating of 30 psi
Materials Used in Valves |  | ||||||||||||
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[Iron-based] Carbon steel and cast iron (An alloy consisting mainly of iron and carbon) Alloy steel (A steel to which one or more alloying elements, other than carbon, (e.g., Ni, Cr, Mn, W and Mo) have been deliberately added to achieve a particular physical property) | [Nonferrous] Copper alloy (Bronze, brass) Light alloy (Any one of various metal alloys consisting mainly of aluminum (Al) or magnesium (Mg) to which one or more alloying elements have deliberately been added (e.g., Cu, Zn, Si)) | [Rubber-based] EPDM (Ethylene-propylene rubber) NBR (Acrylonitrile-butadiene rubber) FKM (Fluoroelastomer) | [Plastic-based] PTFE (Polytetrafluoroethylene) PA (Polyamide resin) | | |||||||||
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