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Model 121 Regulators Brochure

Maximum emergency Pressures

NOTe:

Before using any of the following data, make sure this

entire section is clearly understood.

The maximum pressure the regulator inlet may be subjected
to under abnormal conditions without causing damage to the
regulator is:

¾" through 2½" Pipe Sizes ................................ 70 psi
3" Pipe Size ....................................................... 50 psi
4" Pipe Size ....................................................... 25 psi

The maximum pressure the regulator outlet may be subjected to
without causing damage to the internal parts of the regulator is:

121-8 ................................................. set-point + 5 psi
121-8HP .......................................... set-point + 10 psi
121-12 ............................................... set-point + 5 psi
121-16 ............................................... set-point + 2 psi

6HWSRLQWLVGH¿QHGDVWKHRXWOHWSUHVVXUHDUHJXODWRULVDGMXVWHG

to deliver. If any of the above pressure limits are exceeded, the
regulator must be taken out of service and inspected. Damaged
parts must be repaired or replaced.

The maximum pressure that can be safely contained by the
diaphragm case is:

121-8 ................................................................. 25 psi
121-8HP ............................................................ 25 psi
121-12 ............................................................... 20 psi
121-16 ............................................................... 10 psi

Safely contained means no leakage as well as no bursting.

Over-pressurization Protection

Protect the downstream piping system and the regulator’s low
pressure chambers against over-pressurization due to the
possible regulator malfunction or failure to achieve complete
lockup. The allowable outlet pressure is the lowest of the
maximum pressures permitted by federal codes, state codes,
Sensus bulletin RDS-1498, or other applicable standards. The
method of protection can be a relief valve, monitor regulator,
shutoff device, or similar mechanism.

Full Open Capacity

Capacity of the Model 121 in the full open position can be
calculated using the following formulas and K factors:

1. Q = K

– P

................ (for P

ʘOHVVWKDQ

2. Q =

K P

............................... (for P

ʘJUHDWHUWKDQ

4 )XOORSHQFDSDFLW\LQ6&)+RIVSHFL¿FJUDYLW\

natural gas.

absolute

LQOHWSUHVVXUHSVLD

absolute

RXWOHWSUHVVXUHSVLD

3LSH6L]HRXWOHW

........................................ K=1400

1½" Pipe Size ................................................. K=2750
2" Pipe Size .................................................... K=4750
2½" Pipe Size ................................................. K=5250

ó3LSH6L]HRXWOHW

..................................... K=1750

3" Pipe Size .................................................. K=11000
4" Pipe Size .................................................. K=18000

Remember, at the above full open capacities the droop is

VLJQL¿FDQWO\JUHDWHUWKDQVSHFL¿HGLQWKHFDSDFLW\WDEOHVRQ

pages 4, 5, 6 and 7.

When checking 121 regulator capacity for use in providing
adequate relief capacity, use the above calculated full open
capacity. Do not use 121 capacity values from the tables on
pages 4, 5, 6 and 7.

Pipe Sizes

6FUHZHG137

)ODQJHG$16,

125 lb. FF.

¾" x 1"

1½" x 1½"

2" x 2"

¾" x 1¼"

1½" x 2"

3" x 3"

1" x 1"

2" x 2"