2
K109i
AUG 2015
*
* This factor is not suitable when combustible materials
are within 20 feet (6.1 m) of the pressure vessel; refer to
relevant codes for corrected sizing method.
Example:
To determine the minimum required capacity
of a relief valve for a vessel containing ammonia that
measures 16 feet in length and 6 feet in outside diameter,
the equation would be as follows: 0.5 x 6 x 16 = 48 lb/min.
Step 2:
Determine the pressure setting needed. This
should be at or below the design pressure of the vessel.
The relief setting should also be at least 25% above the
maximum expected operating pressure to avoid “weeping”
of relief valves. The setting may be below (never above) the
design pressure of the vessel, but it is sometimes best to
match vessel design pressure and relief setting to minimize
the likelihood of a discharge.
Step 3:
Refer to the Valve Capacity Ratings below and
select the valve with the required capacity (C) at the desired
pressure setting.
VALVE SIZING AND SELECTION
Step 1:
Use the formula below, per ANSI/ASHRAE 15
Safety Standard for Refrigeration Systems to calculate the
minimum required discharge capacity in pounds of air per
minute. When selecting a dual pressure-relief valve system,
be aware that each individual valve must have sufficient
capacity to protect the vessel.
C=fDL
C =
m i n i m u m r e q u i r e d d i s c h a r g e c a p a c i t y o f
the relief device in pounds of air per minute.
f =
f a c t o r f o r a m m o n i a r e f r i g e r a n t i s 0 . 5 * *,
factor for R-22 and R-134a refrigerants is 1.6**, for
other refrigerants see ANSI/ASHRAE 15 or contact
factory.
D =
outside diameter of vessel in feet.
L =
length of vessel in feet.
O
N
T
A
C
R
I
A
Y
T
I
C
A
P
A
C
)
g
i
s
p
(
S
G
N
I
T
T
E
S
E
R
U
S
S
E
R
P
D
R
A
D
N
A
T
S
0
5
1
5
7
1
0
0
2
5
2
2
0
5
2
5
7
2
0
0
3
5
2
3
0
5
3
0
0
4
R
0
0
6
5
H
R
2
0
6
5
H
n
i
m
/
b
l
5
.
0
1
2
.
2
1
8
.
3
1
4
.
5
1
0
.
7
1
6
.
8
1
2
.
0
2
8
.
1
2
5
.
3
2
7
.
6
2
m
f
c
s
0
4
1
2
6
1
3
8
1
5
0
2
6
2
2
8
4
2
9
6
2
0
9
2
2
1
3
5
5
3
R
2
3
6
5
H
n
i
m
/
b
l
2
2
5
2
9
2
2
3
6
3
9
3
2
4
6
4
9
4
6
5
m
f
c
s
2
9
2
7
3
3
2
8
3
7
2
4
2
7
4
7
1
5
1
6
5
6
0
6
1
5
6
1
4
7
R
3
3
6
5
H
n
i
m
/
b
l
8
2
3
3
7
3
1
4
6
4
0
5
4
5
9
5
3
6
2
7
m
f
c
s
7
7
3
5
3
4
2
9
4
0
5
5
8
0
6
5
6
6
3
2
7
1
8
7
9
3
8
4
5
9
R
4
3
6
5
H
n
i
m
/
b
l
4
3
9
3
4
4
9
4
4
5
0
6
5
6
0
7
5
7
5
8
m
f
c
s
9
4
4
8
1
5
6
8
5
5
5
6
4
2
7
3
9
7
1
6
8
0
3
9
9
9
9
6
3
1
1
A
0
0
6
5
H
n
i
m
/
b
l
3
.
1
3
1
.
6
3
9
.
0
4
7
.
5
4
5
.
0
5
3
.
5
5
1
.
0
6
9
.
4
6
7
.
9
6
3
.
9
7
m
f
c
s
7
1
4
0
8
4
4
4
5
8
0
6
2
7
6
6
3
7
9
9
7
3
6
8
7
2
9
5
5
0
1
1
0
6
5
H
2
0
6
5
H
n
i
m
/
b
l
8
.
5
3
3
.
1
4
8
.
6
4
2
.
2
5
7
.
7
5
2
.
3
6
6
.
8
6
1
.
4
7
6
.
9
7
m
f
c
s
6
7
4
9
4
5
2
2
6
5
9
6
8
6
7
1
4
8
3
1
9
6
8
9
9
5
0
1
3
1
6
5
H
n
i
m
/
b
l
0
.
3
5
1
.
1
6
2
.
9
6
3
.
7
7
4
.
5
8
5
.
3
9
6
.
1
0
1
7
.
9
0
1
8
.
7
1
1
4
3
1
m
f
c
s
4
0
7
2
1
8
0
2
9
8
2
0
1
6
3
1
1
3
4
2
1
1
5
3
1
9
5
4
1
7
6
5
1
2
8
7
1
4
0
6
5
H
n
i
m
/
b
l
0
.
2
7
0
.
3
8
0
.
4
9
1
.
5
0
1
1
.
6
1
1
1
.
7
2
1
1
.
8
3
1
1
.
9
4
1
2
.
0
6
1
2
8
1
m
f
c
s
8
5
9
4
0
1
1
1
5
2
1
7
9
3
1
4
4
5
1
1
9
6
1
7
3
8
1
4
8
9
1
0
3
1
2
3
2
4
2
Important Note: These are atmospheric relief valves. Settings equal pressure above atmosphere when outlet is connected via
proper piping to the atmosphere (outside). (scfm = Standard Cubic Feet per Minute)
INSTALLATION DIMENSIONS
O
N
T
A
C
S
N
O
I
T
C
E
N
N
O
C
D
E
D
A
E
R
H
T
T
P
N
A
(MM)
B
(MM)
C
(MM)
M
O
T
T
O
B
T (DN)
E
L
N
I
E
D
I
S
T (DN)
E
L
T
U
O
A
0
0
6
5
H
R
0
0
6
5
H
1
/
2
T (15)
P
F
"
3
/
4
T (20)
P
F
"
2.13"
(54)
2.75"
(70)
1.63"
(41)
3.00"
(76)
4.13"
(105)
2.25"
(57)
1
0
6
5
H
PT (25)
F
"
1
2
0
6
5
H
R
2
0
6
5
H
R
2
3
6
5
H
3
/
4
T (20)
P
F
"
PT (25)
F
"
1
1
3
1
6
5
H
R
3
3
6
5
H
T (25)
P
F
"
1
1
/
4
T (32)
P
F
"
1
1
/
2
T (40)
P
F
"
4
0
6
5
H
R
4
3
6
5
H
1
1
/
4
T (32)
P
F
"
H5600 “R” Series capacity valves have green installation
date tags, while all others are blue.
A
B
C
PRESSURE-RELIEF VALVE CAPACITY RATINGS (NATIONAL BOARD CERTIFIED)
