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 <1.5 bar (22 psig).

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.