How Pressure Rating Affects Butterfly Valve Choice

Publish Time: 05/25 2026 Author: Site Editor Visit: 26

How Pressure Rating Affects Butterfly Valve Choice: PN, Class, and Selection Guide

Pressure rating determines how much internal pressure a butterfly valve can safely withstand. Selecting the wrong rating leads to seat extrusion, body failure, or unnecessary cost overruns.

This guide covers PN and Class ratings, pressure-temperature derating, and selection by application.

Pressure Rating Standards

Standard	Region	Common Ratings
PN (DIN/EN)	Europe, Asia, International	PN10, PN16, PN25, PN40
Class (ASME)	North America	Class 125, 150, 300, 600
JIS	Japan	5K, 10K, 16K, 20K

PN vs Class – Quick Comparison

Rating	Bar (max)	PSI (max)	Typical Use
PN10	10 Bar	145 PSI	Low pressure water
PN16	16 Bar	232 PSI	Standard HVAC, water
PN25	25 Bar	363 PSI	Industrial, chemical
PN40	40 Bar	580 PSI	High pressure, steam
Class 125	11 Bar	160 PSI	Cast iron (low pressure)
Class 150	20 Bar	290 PSI	Standard ASME
Class 300	50 Bar	725 PSI	High pressure ASME
Class 600	100 Bar	1,450 PSI	Very high pressure

Note: PN16 (16 Bar) and Class 150 (20 Bar) are not equivalent. Verify before substituting.

Pressure Rating by Valve Type

Valve Type	Typical Rating	Max Rating	Limiting Component
Wafer type (rubber seat)	PN10-PN16	PN25 (limited sizes)	Seat extrusion
Wafer type (PTFE seat)	PN16-PN25	PN40	Body strength
Lug type (rubber seat)	PN16-PN25	PN25	Seat + lugs
Lug type (PTFE/metal seat)	PN25-PN40	PN40	Body material
Double offset	PN25-PN40	PN40	Seat design
Triple offset	PN40-PN100+	Class 600+	Metal seat + body

Pressure-Temperature Derating

Maximum pressure decreases as temperature increases. This applies to all butterfly valves.

PN16 Derating (Ductile Iron Body, EPDM Seat)

Temperature (°C)	Max Pressure (Bar)	% of Rating
20°C	16.0	100%
50°C	15.2	95%
80°C	14.0	88%
100°C	12.5	78%
120°C	10.0	63%

PN25 Derating (SS316 Body, PTFE Seat)

Temperature (°C)	Max Pressure (Bar)	% of Rating
20°C	25.0	100%
100°C	23.5	94%
150°C	21.0	84%
200°C	18.0	72%
230°C	14.0	56%

Class 150 Derating (Cast Steel Body, Metal Seat)

Temperature (°F)	Temp (°C)	Max Pressure (PSI)	Max Pressure (Bar)
100°F	38°C	290	20.0
200°F	93°C	260	17.9
300°F	149°C	230	15.9
400°F	204°C	200	13.8
500°F	260°C	170	11.7

Critical rule: Always consult P-T chart for your specific valve material combination.

Seat Material vs Maximum Pressure

Seat Material	Max Pressure (Bar)	Limiting Factor
EPDM	16 Bar	Extrusion at higher pressure
NBR	16 Bar	Extrusion
Viton	16-20 Bar	Extrusion + temperature
PTFE	25 Bar	Cold flow (creep)
Reinforced PTFE	40 Bar	Reduced cold flow
PEEK	40-60 Bar	Very high strength
Metal	40-100 Bar	Body strength

Body Material vs Pressure Rating

Body Material	Max Pressure (Bar)	Max Temperature	Typical Use
PVC / CPVC	10 Bar	60-80°C	Low pressure chemical
Ductile Iron (GGG40)	25 Bar	350°C	General industrial
Cast Steel (WCB)	40 Bar	425°C	High pressure steam
SS316 (CF8M)	40 Bar	650°C	Corrosive high pressure
Duplex	40 Bar	350°C	Seawater, high chloride
Hastelloy	40+ Bar	800°C+	Extreme chemical

Pressure Drop vs Pressure Rating – Do Not Confuse

Term	Definition	Significance
Pressure rating	Maximum safe internal pressure	Safety limit
Pressure drop (ΔP)	Pressure loss across valve	Energy loss, cavitation risk

Common mistake: A valve rated for PN16 can operate at 5 Bar with a 3 Bar pressure drop. The pressure drop does not need to be lower than the rating – only the inlet pressure matters.

Seat Extrusion – The High-Pressure Failure Mode

Seat extrusion occurs when pressure pushes soft seat material into the gap between disc and body.

Pressure	Seat Risk	Prevention
<10 Bar	Low	Standard seat acceptable
10-16 Bar	Moderate (EPDM)	Backup ring or reinforced seat
16-25 Bar	High (soft seat)	PTFE or reinforced seat
25-40 Bar	Very high	Metal seat or PEEK
>40 Bar	Not possible with soft seat	Metal seat only

Extrusion Prevention Features

Feature	Effect
Backup ring	Supports seat at high pressure
Reinforced PTFE (glass/carbon)	Reduces cold flow
Hard seat (PEEK)	Resists extrusion
Metal seat	No extrusion

Selection by System Pressure

System Pressure (Bar)	Recommended Valve Type	Seat Material
0-6 Bar	Any type	EPDM, NBR, Viton
6-10 Bar	Any type	EPDM, Viton, PTFE
10-16 Bar	Wafer or lug	EPDM with backup ring, PTFE
16-25 Bar	Lug or flanged	PTFE, reinforced PTFE
25-40 Bar	Double offset, lug	Reinforced PTFE, PEEK, metal
40-60 Bar	Triple offset, flanged	Metal seat (stellite)
60-100 Bar	Triple offset only	Metal seat, special design

Quick Selection Table by Application

Application	Typical Pressure	Recommended Rating
HVAC chilled water (low rise)	3-6 Bar	PN10 or PN16
HVAC chilled water (high rise)	8-12 Bar	PN16 or Class 150
Boiler feedwater	10-20 Bar	PN25 or Class 150/300
Steam distribution	5-15 Bar	PN25 (Class 150)
Chemical transfer	4-10 Bar	PN16 (lined)
Chemical reactor	10-25 Bar	PN25-PN40 (alloy)
Oil pipeline	15-30 Bar	Class 150-300
Gas transmission	20-50 Bar	Class 300-600
Fire protection	10-16 Bar	PN16 or Class 150
Seawater cooling	2-8 Bar	PN16 (Duplex body)
High pressure water jet	40-100 Bar	Class 300-600

Oversizing Pressure Rating – Cost Impact

Selecting a higher pressure rating than needed increases cost unnecessarily.

Valve Size	PN16 Price	PN25 Price	PN40 Price
DN100	$85	$120	$180
DN150	$150	$210	$320
DN200	$280	$390	$580
Premium for PN25	—	+40-50%	—
Premium for PN40	—	—	+100-120%

Cost-saving tip: Match pressure rating to system pressure, not pipe rating. Pipe may be rated higher than needed.

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