Liquid solenoid valve mystery

[mohamed khamis]

Could any body give me an explanation for this performance of the liquid solenoid valve. when it was tested outside the refrigeration cycle it worked properly but when it was installed it is stuck and after 10 minutes when the current supply is given again to the valve elect. coil the valve opens and works. I changed the elect coil from 11 W (0.45 Amp & 24 V) to 20 W (0.8 Amp & 24 V) the same problem is existing. Although the manufacturer's catalog 's recommended coil of 11 W for this solenoid valve. So any body can explain what is happened and how to solve/ avoid this problem. Unfortunately, the maximum power is 20 W for this brand (which is working in hazardous area) and after that we have to go to AC not DC.

Any participation is highly appreciated

Best regards'

Mohamed

[US Iceman]

Is it a direct-acting solenoid or one that is pilot-operated?

[Peter_1]

Was it installed in the right direction?

[mohamed khamis]

Ok thanks all for your participation it was instated correctly and it is pilot type EVR 20. During the pump down time the discharge pressure reaches 280 PSI and suction pressure 30 PSI this after the solenoid valve closing directly. however, as it was observed that during valve activation to run the system only a very low magnetic field you can feel. And when it is stopped and waiting for almost 10 minutes until the discharge pressure reaches 200 PSI and suction 100 PSI when the valve is activated at this condition it works well. I think that the low magnetic field makes the valve plunger to lift up little bit and infiltration of refrigerant escapes from the upper diaphragm of the valve to the lower side and so the pressure reaches to this value of 200 PSI and 200 PSI. At this moment the restrained pressure above the diaphragm has been released and the diaphragm goes up making full opening for the valve. However, what makes me confused why the plunger was not drawn up although the resistive force is only its weight and the spring force. I wonder the restrained pressure 250 PSI has an influence on the plunger also or not. And why the magnetic field is very low at this moment, any body can explain to me this dilemma and what is the proper solution and many thanks in advance.

Regards
Mohamed

[BESC5240]

EVR20 is the valve largest with a diaphragm in this range. (the lift of the diafragm is the highest in this range)
Maximum opening pressure differential with a 20 Watt DC coil is 16 bar (approx. 230 psi) ...
Which coil do you use (code number)?

[NoNickName]

The plunger seating is magnetic-permeable. When the coil is dc, the seating magnetises and remains magnetised even when the coil is not engaged, especially in train installations because of the dc field of airwire. Therefore the seating pulls the plunger.
Increasing the power of the coil doesn't help because the field is applied on the plunger, but also over and under it.
The only possibility is to increase the voltage (if 24 Vdc, apply 30 or more volts, of 110 Vdc, apply 150 or more Vdc). This does not happen with ac coils.

[mohamed khamis]

EVR20 is the valve largest with a diaphragm in this range. (the lift of the diafragm is the highest in this range)
Maximum opening pressure differential with a 20 Watt DC coil is 16 bar (approx. 230 psi) ...
Which coil do you use (code number)?

ok thanks for your input I used firstly a coil of 12 DC W the number is code 018z6596 then when it was not able to work properly. I changed the coil to 20 DC W and the code number is 018F6857. could u clarify what do u mean Maximum opening pressure differential is 16 bar. As I understand that the difference between the pressure before the diaphragm (outlet from the condenser) and the pressure after diaphragm (inlet to TXV) is 16 bar or what?. Once again I do appreciate ur participation

[mohamed khamis]

The plunger seating is magnetic-permeable. When the coil is dc, the seating magnetises and remains magnetised even when the coil is not engaged, especially in train installations because of the dc field of airwire. Therefore the seating pulls the plunger.
Increasing the power of the coil doesn't help because the field is applied on the plunger, but also over and under it.
The only possibility is to increase the voltage (if 24 Vdc, apply 30 or more volts, of 110 Vdc, apply 150 or more Vdc). This does not happen with ac coils.

Thanks but the supply current comes from PLC and this refrigeration system is installed in offshore (oil &gas plant) and it must be DC and explosion proof. The PLC apply only 24 VDC. Any another solution will be highly appreciated.

[NoNickName]

Thanks but the supply current comes from PLC and this refrigeration system is installed in offshore (oil &gas plant) and it must be DC and explosion proof. The PLC apply only 24 VDC. Any another solution will be highly appreciated.

Is it really 24Vdc? or something less that 24....?
Do you have big iron parts in the vicinity?
Do you have big DC buses in the vicinity?

Try a 12Vdc coil or change the power supply to 24Vac.

[BESC5240]

ok thanks for your input I used firstly a coil of 12 DC W the number is code 018z6596 then when it was not able to work properly. I changed the coil to 20 DC W and the code number is 018F6857. could u clarify what do u mean Maximum opening pressure differential is 16 bar. As I understand that the difference between the pressure before the diaphragm (outlet from the condenser) and the pressure after diaphragm (inlet to TXV) is 16 bar or what?. Once again I do appreciate ur participation

018Z6596 is a 10 W DC coil (for Atex application). You should use at least this 20 W DC coil (018F6857).

You should also make sure that you have the 'DC-version' of the valve. The plunjer (or armature, as we call it) is different from an AC-version: it is round, in stead of a square; this gives a bigger surface for the magnetic flux (and will increase the electromagnetic pulling force).

MOPD is the maximum pressure difference between the inlet and the outlet of the valve. Due to the construction, each valve has it's MOPD, depending on the coil used.

[mohamed khamis]

Is it really 24Vdc? or something less that 24....?
Do you have big iron parts in the vicinity?
Do you have big DC buses in the vicinity?

Try a 12Vdc coil or change the power supply to 24Vac.

It is theoretically 24 VDC but practically 22 to 23 VDC


No big iron parts nor big DC buses. are you sure the change to 12 VDC will help...The using of AC source is quite restricted in hazardous area such as offshore oil and gas platform, pls suggest

[BESC5240]

It is theoretically 24 VDC but practically 22 to 23 VDC

The relation between the pulling force, K and the voltage applied, U is:

K=k.(U/R)²

So a drop in voltage of 10% will lead to a drop in force of 20% (19%).

Also the temperature has an on fluence on K. (since it influences R ...

[NoNickName]

It is theoretically 24 VDC but practically 22 to 23 VDC


No big iron parts nor big DC buses. are you sure the change to 12 VDC will help...The using of AC source is quite restricted in hazardous area such as offshore oil and gas platform, pls suggest

try. The worst scenario is that you will burn the coil. CAREFUL: it will draw twice the current, so the output of your plc may suffer if not sized properly.

[mohamed khamis]

Thank you all for your participation

BESC5240,

Ok when I checked the coil selection with the electrical engineer I found out that the coil code is for AC-version but there is some thing confuses me that I am going to use the same valve model in another project and when I checked the plunger/armature shape I found it is a round. this means this model for DC-version, wright or wrong?. So r u sure that the cross section for DC-version is round?. Once again my appreciation to you all guys

Regards
Mohamed

[NoNickName]

Yes, DC is round, AC is square.

[monkey spanners]

Would swapping the live and neutral make any difference to the magnetic field generated? If so you could swap the live and neutral connections on each switching with a relay arangement.

[nike123]

Would swapping the live and neutral make any difference to the magnetic field generated? .

No, field changes his direction by frequency of source AC.

[NoNickName]

Note that the power supply is DC not AC.

[nike123]

Note that the power supply is DC not AC.

If you are referring to my answer, note that "Live" and "Neutral" are terms used in AC power supply!
Positive and Negative are correct terms for DC current.

[NoNickName]

If you are referring to my answer, note that "Live" and "Neutral" are terms used in AC power supply!
Positive and Negative are correct terms for DC current.

Yes, but this guy has got DC solenoid valve, not AC, so your comment is off topic.

[nike123]

Yes, but this guy has got DC solenoid valve, not AC, so your comment is off topic.

I was quoted text at which I was referring in my answer!
So, as you see, it is not answer to original poster, it is answer to monkey spanners question, and therefore it is not off-topic.