Emerson EZH and EZHSO Series Pressure Reducing Regulators Ficha de datos descargar pdf (Pagina 3)

Bulletin 71.4:EZH

Principle of Operation

A pressure relief valve is a throttling pressure control device

that opens and closes to ensure the downstream pressure

does not rise above a predetermined pressure. Fisher

relief valves cannot be used as ASME safety relief valves.

A backpressure regulator is a device that controls and

responds to changes in the upstream pressure. It functions

the same as a relief valve in that it opens on increasing

upstream pressure.

Relief Valve

As long as the inlet pressure is below the set pressure, the

pilot control spring keeps the pilot valve plug closed. Inlet

pressure passes through the restrictor and registers as

loading pressure on the main valve diaphragm chamber.

Force from the main spring, in addition to pilot loading

pressure, provide loading pressure to keep the main valve

diaphragm and plug assembly tightly shut off. When the

inlet pressure rises above the set pressure, the pressure

on the pilot diaphragm overcomes the pilot control spring

and opens the pilot valve plug. The pilot then exhausts the

loading pressure from the main valve diaphragm chamber.

The pilot continuously exhausts gas when the inlet pressure

is above the set pressure. The inlet pressure unbalance

overcomes the main spring force and opens the diaphragm

and plug assembly.

As the inlet pressure drops below the set pressure, the pilot

control spring closes the pilot valve plug and the exhaust

to atmosphere stops. Force from the main spring, along

with pilot loading pressure, pushes the diaphragm and plug

assembly onto the knife-edged seat, producing tight shutoff.

Backpressure Regulator

As long as inlet pressure remains below setpoint, the

pilot control spring keeps the pilot valve plug closed. Inlet

pressure passes through the upper port around the upper

portion of the valve plug and then through the hollow

passage in that valve plug. Force from the main spring,

in addition to pilot loading pressure, provide downward

loading pressure to keep the main valve diaphragm and plug

assembly tightly shut off. When inlet pressure rises above

the set pressure, pressure on the pilot diaphragm overcomes

the control spring to close the upper port and stroke the

valve plug to open the lower port. The pilot exhausts loading

pressure from the main valve diaphragm chamber. Inlet

pressure unbalance overcomes the main spring force to

open the diaphragm and plug assembly.

While the main valve is throttling, the upper port of the pilot

stays closed. The pilot exhausts only when it repositions the

main valve. As inlet pressure drops below setpoint, the pilot

control spring overcomes the diaphragm force to stroke the

valve plug down to close the lower port and open the upper

port. Force from the main spring, along with the pilot loading

pressure, pushes the diaphragm and plug assembly onto the

knife-edged seat, producing tight shutoff.

Capacity Information

Note

EZH Series ow capacities are laboratory

veried; therefore, it may be sized for 100%

ow using published capacities as shown. It is

not necessary to reduce published capacities.

Table 7 show the natural gas regulating capacities of the

Type EZH relief or backpressure regulator at selected

inlet pressures and outlet pressure settings. Flows are in

thousands of SCFH at 60°F and 14.7 psia (or in thousands

of Nm³/h at 0°C and 1.01325 bar) of 0.6 specic gravity

natural gas.

To determine equivalent capacities for air, propane, butane

or nitrogen, multiply the capacity by the following appropriate

conversion factor: 0.775 for air, 0.628 for propane, 0.548

for butane or 0.789 for nitrogen. For gases of other specic

gravities, multiply the given capacity by 0.775 and divide by

the square root of the appropriate specic gravity. Then, if

capacity is desired in Nm³/h at 0°C and 1.01325 bar, multiply

SCFH by 0.0268.

To nd approximate regulating capacities at pressure

settings not given in Table 7 or to nd wide-open ow

capacities for relief sizing at any inlet pressure, perform one

of the following procedures. Then convert using the factors

provided above, if necessary.

Critical Pressure Drops

For critical pressure drops (absolute outlet pressure equal

to or less than one-half of absolute inlet pressure), use the

following formula:

Q = (P

)(C

)(1.29)

Non-Critical Pressure Drops

For pressure drops lower than critical (absolute outlet pressure

greater than one-half of absolute inlet pressure).

Q =

520

SIN

3417

DEG

where,

Q = gas ow rate, SCFH

= absolute inlet pressure, psia (P

gauge + 14.7)

= regulating or wide-open gas sizing coefcient

G = gas specic gravity of the gas

T = absolute temperature of gas at inlet, °Rankine

= ow coefcient

P = pressure drop across the regulator, psi

1 2 3 4 5 6 7 8

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Emerson EZH and EZHSO Series Pressure Reducing Regulators Ficha de datos Pagina 3

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