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PSV data sheet explained

A pressure safety valve (PSV) data sheet carries everything needed to size, build, and test one valve. This page explains each line of a typical EPC data sheet and who fills it in. A blank copy is ready to download in Excel and PDF.

The short answer

The purchaser fills in the process lines: service, fluid and phase, required capacity, set pressure, back pressure, temperatures, and the design code. We fill in the lines that follow from sizing: calculated and selected area, orifice letter, spring, and serial numbers.

A sheet with the process lines complete is enough for us to size the valve and quote it.

How the sheet is laid out

Many EPC data sheets use a layout like this one, and the line numbers on your project's sheet may differ. One sheet covers one tag number. The lines are numbered 1 to 65 and grouped into eight blocks, with five numbers left blank between blocks. Where one line holds two fields, the tables below list both under the same number.

The last column of each table says who usually fills in the line. Your project may assign the lines differently:

Purchaser
The EPC contractor or the end user, usually the process engineer who owns the relief case.
Manufacturer
The valve maker, Luofu, after sizing. Data sheets often mark these lines VTA, vendor to advise.
Purchaser or manufacturer
The purchaser states a value when the project specification sets one. If not, we propose a value and the purchaser confirms it. Data sheets often mark these lines VTC, vendor to confirm.

The blank data sheet on this page uses the same lines and blocks.

General, lines 1 to 13

The first block identifies the valve and states what kind of valve the duty calls for.

Line Field What to enter Filled in by
1 Tag number The tag of the valve on the P&ID, for example PSV-1001. Use one sheet per tag. Purchaser
2 Service A short name for the duty, such as hydrocarbon gas or cooling water. Purchaser
3 P&ID number The drawing that shows the valve and the equipment it protects. Purchaser
4 Design (safety, relief, or safety relief) A safety valve opens fully at once and suits gas, vapor, and steam. A relief valve opens in proportion to the pressure rise and suits liquid. A safety relief valve can do either. Purchaser
5 Type (conventional, bellows, or pilot-operated) Back pressure usually decides the type. See lines 27 to 29 and back pressure and valve type. Purchaser or manufacturer
6 Bonnet type Closed or open. A closed bonnet keeps the discharge inside the valve and the outlet pipe. Open bonnets are common on steam service. Purchaser or manufacturer
7 Ambient temperature Lowest and highest air temperature at site, in °C. The lowest value matters for materials of valves installed outdoors. Purchaser
8 Allowable sound pressure level The noise limit for the discharge, in dBA, at the distance the project specification sets. Line 42 gives the calculated level to compare. Purchaser
9 Balanced valve (yes or no) Yes when back pressure is high or varies, so that it must not shift the set pressure. A bellows or a pilot valve does this. Purchaser or manufacturer
10 Spare valve (yes or no) Yes when an installed spare is needed, so that one valve can come out for service while the other protects the equipment. Spare pairs often sit on a changeover valve. Purchaser
11 Upstream rupture disc required (yes or no) Yes when a rupture disc is installed under the valve inlet. The capacity of the pair then takes a combination factor. Purchaser
12 Rupture disc tag number The tag of that rupture disc, or N/A. Purchaser
13 Relief contingency The case that sets the required capacity, such as blocked outlet, external fire, or thermal expansion. See relief cases. Purchaser

Line and equipment, lines 14 to 19

This block ties the valve to the piping and the equipment it protects.

Line Field What to enter Filled in by
14 Line number The line the valve connects to. Purchaser
15 Pipe class The piping specification of that line. It gives the flange rating, facing, and line materials the valve must match. Purchaser
16 Equipment number The vessel or other equipment the valve protects. Purchaser
17 Line size Nominal size of the inlet line, NPS or DN. Purchaser
17 Line schedule Wall schedule of the inlet line, for example SCH 80. Purchaser
18 Line material The pipe material, for example ASTM A106 Grade B. The body material is usually chosen to suit it. Purchaser
19 Pipe insulation thickness Thickness of the insulation on the line, or N/A. Purchaser

Process conditions, lines 20 to 36

These lines feed the sizing equations. Give values at relieving conditions where the line asks for them, and state the unit next to each value.

Line Field What to enter Filled in by
20 Fluid The medium, for example natural gas, hydrogen, or crude oil. Purchaser
20 Phase Gas or vapor, liquid, steam, or two-phase, at relieving conditions. The phase decides the sizing method. Purchaser
21 Required capacity The flow the valve must pass in the governing case, in kg/h. Liquid cases may give m³/h. Purchaser
22 Operating specific gravity Specific gravity of a liquid at operating temperature. Purchaser
22 Corrosive, erosive, or toxic components Name them, for example H2S, chlorides, or solids. They decide the materials, the bellows, and the bonnet. Purchaser
23 Operating pressure, normal The normal pressure at the valve inlet, in bar(g). The margin to the set pressure matters for seat tightness. Purchaser
24 Operating temperature The normal temperature at the valve inlet, in °C. A range is fine. Purchaser
25 Set pressure The inlet gauge pressure at which the valve starts to open, in bar(g). The applicable code relates it to the MAWP of the protected equipment. Purchaser
26 Relieving temperature The fluid temperature at relieving conditions, in °C. It sets gas density and material limits. Purchaser
27 Back pressure, constant Superimposed back pressure that is present before the valve opens and does not change, in bar(g). Purchaser
28 Back pressure, built-up Back pressure that builds in the outlet piping while the valve discharges. The limit for a conventional valve comes from the applicable code. Purchaser
29 Back pressure, total Superimposed plus built-up back pressure. It decides the back pressure correction on line 59. Purchaser
30 Allowable overpressure The pressure rise above set pressure allowed during relief, in percent. The applicable code sets the value for one valve, for several valves, and for an external fire case. Purchaser
30 Latent heat of vaporization For fire cases on liquid-filled equipment, in kJ/kg. The fire heat input divided by it gives the vapor flow. Purchaser
31 Compressibility factor Z of the gas at relieving conditions. Purchaser
31 Overpressure factor A capacity correction used in some liquid sizing methods when the overpressure differs from the certified one. Leave it blank if your basis does not use it. Purchaser or manufacturer
32 Design pressure, maximum and minimum Design pressure of the protected equipment, in bar(g), and the minimum if it has one, such as full vacuum. Purchaser
33 Relief viscosity Viscosity at relieving conditions, in cP. Viscous liquids take a viscosity correction. Purchaser
33 Relief density Density at relieving conditions, in kg/m³. Purchaser
34 Barometric pressure Atmospheric pressure at site, in bar(a). Sizing adds it to the relieving pressure. Purchaser
34 Ratio of specific heats (Cp/Cv) k of the gas at relieving conditions. It sets the gas flow coefficient in the sizing equation. Purchaser
35 Design temperature, maximum and minimum Design temperatures of the protected equipment, in °C. The minimum decides low-temperature materials and impact testing. Purchaser
36 Molecular weight Of the gas or vapor, in kg/kmol. Purchaser

If a value is not known yet, write TBC and give your best estimate in the notes. Preliminary values are fine for a first sizing.

Basis and selection, lines 38 to 43

This block records the code and the sizing result. Most of it is our answer to the process data above.

Line Field What to enter Filled in by
38 Design code The code the valve must meet, for example ASME, and whether it must carry the ASME UV stamp. Purchaser
39 Sizing basis The method behind the area, usually API 520. Purchaser or manufacturer
39 Case The relief case used for sizing. It repeats line 13. Purchaser
40 Calculated area Minimum flow area from the sizing, in cm². A separate fire case area is listed when it differs. Manufacturer
41 Selected area Effective area of the selected orifice. It is equal to or larger than the calculated area. Manufacturer
42 Orifice designation The letter of the selected orifice, D to T. See API 526 orifice sizes. Manufacturer
42 Calculated sound pressure level Noise of the discharge from the calculation, in dBA, to compare with line 8. Manufacturer
43 Overpressure cause The event behind the overpressure, often the same as line 13. Purchaser
43 Coefficient of discharge Kd of the selected valve. Sizing starts with an effective value and the final check uses the certified value. Manufacturer

Connections, lines 45 to 49

Line 45 is a column heading. From line 46, each line holds one value for the inlet and one for the outlet.

Line Field What to enter Filled in by
46 Size Inlet and outlet size, NPS or DN. The outlet is larger than the inlet on most valves. Sizing confirms both. Purchaser or manufacturer
47 Rating Flange class of the inlet and the outlet, for example Class 300 inlet and Class 150 outlet. Purchaser
48 Facing Flange face type and finish, for example raised face 125 to 250 AARH, or ring joint. Purchaser
49 Inlet and outlet connection type Flanged, threaded, or welded. Purchaser

Materials, lines 51 to 54

State the materials the project specification requires. Where it leaves a part open, we propose a material for the medium and the temperature range.

Line Field What to enter Filled in by
51 Body and bonnet The pressure-containing parts, usually matched to the line material. Purchaser or manufacturer
51 Seat and rings Nozzle, disc, and nozzle ring materials. Hard facing such as Stellite is common on the seat. Purchaser or manufacturer
52 Resilient seat seal Soft seat material if one is used, for example PTFE, or N/A for a metal seat. Purchaser or manufacturer
52 Guide and rings Guide and guide ring materials. Purchaser or manufacturer
53 Spring Spring material, chosen for the temperature and the medium. Manufacturer
54 Pilot material Pilot body and trim material for a pilot-operated valve, or N/A. Purchaser or manufacturer

Options, lines 56 to 59

Options cover the top works of the valve, testing, and the back pressure correction.

Line Field What to enter Filled in by
56 Cap, screwed or bolted How the cap fastens to the bonnet. Purchaser or manufacturer
56 Test gag Yes if a gag is needed to hold the valve shut during a hydrostatic test of the system. Purchaser
57 Lever, plain or packed A lifting lever opens the valve by hand for a test. A packed lever seals the cap, so it suits a closed bonnet with back pressure. Purchaser
57 Valve serial number Given by us. Manufacturer
58 Spring range The set pressure range of the selected spring. Manufacturer
58 Spring serial number Given by us. Manufacturer
59 Back pressure capacity correction factor, vapor or liquid Kb for gas and vapor, or Kw for liquid, at the back pressure on line 29. Manufacturer

Purchase, lines 61 to 65

The last block is filled in at order and after manufacture.

Line Field What to enter Filled in by
61 Supplier The company that supplies the valve. Purchaser
62 Manufacturer The company that makes the valve, Luofu Valve Group Co., Ltd. Manufacturer
63 Model Our series and model code. Manufacturer
64 Purchase order number The order the valve belongs to. Purchaser
65 Serial number Serial number of the delivered valve. Manufacturer

Notes under the lines

The notes under the lines carry what the lines cannot hold. We read every note as part of the sheet. Typical notes give:

  • The discharge destination, such as a flare header or atmosphere
  • Gasket and bolting specifications for the flanges
  • A static head to add to the set pressure
  • Values that are still preliminary and will be confirmed later

When preliminary values are confirmed, send the revised sheet. We check the sizing again against the new revision.

Download a blank data sheet

The blank data sheet has the same lines and blocks as the tables above. Shaded lines are the ones we fill in. Fill in one sheet per tag number and email it to us.

No data sheet yet?

Send what you have. Medium, set pressure, required capacity, back pressure, and relieving temperature are enough to start. We ask for the rest by email.

Questions engineers ask

Do I need a completed data sheet before I ask for a quotation?

No. Five items are enough to start: medium and phase, set pressure, required capacity, back pressure, and relieving temperature. We reply with the lines still missing. A completed sheet saves a round of emails.

What do VTA and VTC mean on a data sheet?

VTA means vendor to advise. We fill in that value. VTC means vendor to confirm. The purchaser gives a value, and we confirm it or propose another.

Is there a PSV data sheet template in Excel?

Yes. The blank data sheet on this page comes in Excel and PDF, with the same lines as the tables above. You can also send the data sheet form of your own project.

Can one data sheet cover several valves?

Use one sheet per tag number. Valves in the same service still differ in set pressure, capacity, or back pressure. A cover page can list all tags with their sheet numbers.

API 526 orifice sizes

Orifice letters D to T, their effective areas, and how a size code such as 3K4 reads.

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