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Help CenterDanfoss Solenoid Valves, Two-step On/off Types PMLX32-40,PMLX50-65,PMLX100-125
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Danfoss Solenoid valves, two-step on/off Types PMLX32-40,PMLX50-65,PMLX100-125 Introduction
PMLX are 2-step servo-operated main valves with screwed-on pilot solenoid valves. PMLX valves use an external pressure source for opening (which means that no differential pressure across the PMLX valve is required).
PMLX are used in suction lines for the opening against high differential pressure, e.g. after hot gas defrost in large industrial refrigeration
systems with ammonia or fluorinated refrigerants.
PMLX opens in two steps:
Step one opens to approx. 10% of the capacity, when the pilot solenoid valves are activated.
Step two opens automatically after the pressure differential across the valve reaches approximately 1.5 bar.
Danfoss Solenoid valves, two-step on/off Types PMLX32-40,PMLX50-65,PMLX100-125 Features
Can be used for all normal, non-flammable refrigerants, including R 717, and non-corrosive gases/liquids - assuming seals of the correct material are used. Large range of flanges with connection dimensions in accordance with standards: DIN,ANSI, SOC and SA.Inexpensive and simple installation.
Screw thread pilot valve fitting.Only one signal required for both pilot
solenoid valves. The valve has a pressure gauge connection so that inlet pressure can be measured. The PMLX main valve top cover can be oriented in any direction without the function of pilot valves being affected. The valve can be equipped with an AKS 45 electronic position indicator as an accessory.Especially suitable for systems where low pressure drop is required. Stabilizes working conditions and eliminates pressure pulsations during opening after defrosting. Provides safety against pressure "shocks" as the valve can only open fully when ∆p
Danfoss Solenoid valves, two-step on/off Types PMLX32-40,PMLX50-65,PMLX100-125 Design
Connections
There is a very wide range of connection
possibilities with PMLX main valves:
Welding, DIN (2448)
Welding, ANSI (B 36.10)
Welding socket, ANSI (B 16.11)
Solder connection, DIN (2856)
Solder connection, ANSI (B 16.22)
Refrigerants
Can be used for all normal, non-flammable
refrigerants, including R 717, and non-
corrosive gases/liquids - assuming seals of the
correct material are used.
Use with flammable hydrocarbons cannot be
recommended; please contact Danfoss.
Temperature range
–60/+120°C (–76/+248°F).
Surface
PMLX 32 - 65:
The external surface is zinc-chromated to give
good protection against corrosion.
PMLX 80 - 125:
The surface of the PMLX 80 - 125 is treated
with a multi-layer painting.
Pressure range
The valve is designed for:
Max. working pressure: 28 bar g
(406 psig)
Test pressure: 42 bar g (609 psig)
Opening differential pressure:
0 bar g (0 psig) as valve is kept open by
external pilot pressure.
Max. (MOPD), solenoid valves only
(10 W a.c. [NC] /12 W a.c. [NO] or 20 W d.c.):
21 bar g (305 psig).
The PMLX main valve top cover can be oriented
in any direction without the function of pilot
valves being affected.
Valve body
EN-GJS-400-18-LT
Seals
Do not contain asbestos.
Danfoss Solenoid valves, two-step on/off Types PMLX32-40,PMLX50-65,PMLX100-125 Function
The valve is used as a shut-off valve in suction
lines to open after hot gas defrost.
Since PMLX uses external pilot pressure, the valve
will be open even if the differential pressure is 0.
PMLX must not be used in pipe systems where
the differential pressure across the main valve
in open position can exceed 1 bar (15 psig),
otherwise the step two on the valve will close.
The pilot solenoid valve (pos.15a) allows external
pilot pressure (p 2 ) to the top of the servo piston
and thus opens the first step corresponding to
approx. 10% of the valve capacity. At the same
time the spring, (pos. 23), will be compressed.
This will start a pressure equalization of the inlet
pressure (p 1 ) to the outlet pressure (p 4 ). When the
differential pressure across the valve has fallen to
approx. 1.5 bar (22 psig) the spring will be strong
enough to open the second step and open the
valve for full capacity.
This way high-pressure pulsations, which would
occur when opening for full capacity in one step,
can be avoided.
The exact time taken from when the pilot valves
change position to complete closing of the PMLX
will depend on temperature, pressure, refrigerant
and size of valve. Thus an exact closing time for
the valves cannot be given but, in general, lower
temperatures give longer closing times.
It is very important to take the closing times
into consideration when hot gas defrost is
performed on evaporators. Steps must be taken
to ensure that the hot gas supply valve is not
opened before the PMLX in the suction line is
completely closed. If the hot gas supply valve
is opened before the PMLX in the suction line
is closed, considerable energy will be lost and
potentially dangerous situations might arise
because of “liquid hammer”. In PMLX valves, the
spring-loaded second stage might be induced to
hammer by gas and liquid being forced through
the valve at ∆p > 1.5 bar across the PMLX. The
final result could be severe damage to the valve.
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