Reversal Valve Problem, 1

[Fernando79]

We have a Farval greasing system to our equipment. The reversing valve is FR10 if any one knows that, and the coil resistance around 3 Ohms ,
We faced a problem that we cant put a fuse in the output of the transformer less than 10 Amps
Even though the transformer is 250VA , the problem rises when the pressure switch on all the time It burns the transformer and we will lose the coil of the valve even more all the starter fuses will blown
the Transformer voltage is 110 and if the Pressure switch has a problem and no one see that the Transformer will burnt out , any ideas what shall I do ??

F

 

[CJCPE]

Install a fuse for the valve. Put in an alarm and/or interlock relay that drops out if that fuse blows.

Why can't you put the proper size fuse in the transformer secondary? If it is because the fuse blows on load transient currents, put in a slow blow, time delay fuse. If it is because the fuse holder is too large, put in the proper fuse holder.

 

[CJCPE]

If load transients cause a properly sized time delay fuse to blow, put in a bigger transformer.

 

[Fernando79]

120(v)/3(Ohm)=40 Amps , the Pressure switch located in the end of the greasing Pipes , when we have pressure high it will switch for 3 Seconds Max , and reverse the pumping position , the proper fuse for the transformer is 2.5 A
but it will not work less than 10 Amps , cause the current during the switching ?!!!
if the PS was okay , every thing will be fine even the fuses for the transformer output should be 2.5A , but the problem is big if the PS shorted and the current goes through the valve

What do you mean by time delay fuse?? I never heard about that and how much time u can put in this type??

Thanks for your help

F

 

[Fernando79]

I agree that bigger Transformer will solve the problem but it will be high cost !! since we have more than 10 Greasing pumps and all of them the same problem , 10 AMP fuse for 250VA, and we had 2 pumps the transformer blown out and causes a small fire !!!

any advice will be appreciated ,
PS: if you want to see the Drawing I can send.

Thanks Again

Fernando

 

[CJCPE]

Delay fuses have a time vs. current curve that prevents the fuse from blowing until some time has passed at any overcurrent level. They are widely used for loads that have a high current for a short time when switched on. Check with your supplier.

You can not calculate valve current from V/R. The valve coil inductance must be considered. I doubt that it has 3 ohms impedance at the power frequency.

 

[Fernando79]

I measured the resistance and it was 3 Ohms , however the other terminal of the coil is connected with the ground ,
so how much the current will be in this case ???
how much time these fuses will pass on ??

 

[CJCPE]

If you measured 3 ohms with an ohmeter, that is the DC resistance. The total impedance to AC voltage including both inductance and resistance must be much higher. You need to find the normal coil current or AC impedance from Farval or their catalog or spec sheet. If you have spare parts, perhaps there is data on the box. Or look carefully at a new valve the current rating may be marked somewhere.

 

[Fernando79]

Okay I will check the rated current , but let us assume the current is 10 AMPS , and I have Transformer 2.5 AMP
what shall I do in this case ??

F

 

[CJCPE]

If the valve is only supposed to be energized for a very short time, install a low current time delay fuse that feeds just the valve along with an alarm.

 

[Fernando79]

Do you know how much time this Fuses will be ? and any suggestion for type or manufacturer ??


F

 

[CJCPE]

I think time delay fuses are availabe from a lot of manufacturers. If you search the internet with Google etc. you can probably find them. Time-current curves may be available on the internet also.

I need to leave soon. I hope some others respond to this post.

 

[jraef]

Follow what CJCPE was telling you, he is dead on.

AC coils have what is called an "inrush" when you first turn them on. Because of this, fuse manufacturers have what are called "Time Delay" (aka Slow Blow) fuses that allow an initial inrush without blowing the fuse link. While technically you can get into the specific engineering data of the fuse to see the time curves etc., in reality the fuse manufacturers have thoroughly investigated most AC coil applications and know what the delay needs to be. So if you just get an off-the-shelf TD fuse, rated for the coil current of your solenoid, then you will probably be fine. Post the type of fuse you're using know and we can get an idea of the fuse-holder you currently have, which then tells us the TD type fuse you will need.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Another possible problem is voltage drop. If your conductors are too long, sized too small or both, the valve may not pull in and some designs will draw several times normal current when they don't have enough voltage to pull in properly.
Re the cost of Time Delay fuses, less than a transformer.
However, that is like getting a bigger bandaid. If the valves are causing the transformers to burn up, there is a basic design flaw. If you don't find and fix the design flaw you will just blow fuses instead of transformers. It will get expensive.
respectfully

 

[itsmoked]

What I am seeing is exactly what waross is saying. A slow pull in is the cause of the problem. It could be because of a voltage drop from wire size, transformer sag, or maybe a clogged greasing system.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[CJCPE]

Fernando79:

In your 2nd post you wrote:

"if the PS was okay , every thing will be fine even the fuses for the transformer output should be 2.5A , but the problem is big if the PS shorted and the current goes through the valve"

If this is happening repeatedly, there must be a problem that is causing it. It could be that excessive current due to slow puul-in is welding the contacts. Whatever the cause, it needs to be corrected.

 

[rbulsara]

Fernando79:

Did you ever contacted the manufacturer of the Greasing system? They are the best people to help you here. With all due respect electrical does not appear to be your field of expertize. Hire someone who knows the greasing system and electrical systems. Start with the manufacturer.

 

[CJCPE]

There is a manual for the Farval reversing valve at farval.com. It appears that they supply the valve and pressure switch installed and wired in a "central station" unit. The specifications list the inrush current as 11 amps and the holding current as 1.65 amps. I suspect that is for 120V 60Hz. It appears that there are two solenoids and one or the other is always energized. That would indicate that the valves are a continuous load on the transformer of about 200 VA.

The complete valve model number is FR-10-5(or 9)-volts-Hz. You should check to make sure that you have the correct valve for your voltage and frequency. If you have 50 Hz on a 60 Hz valve, the solenoids would draw too much current.

You should also check the total load on your transformer. The valves alone represent 80% of the loading. A control transformer that is designed to supply starters etc. is designed to supply something like 10 times the VA rating for a very short time to accomodate inrush current without the voltage dropping too much.

 

[Fernando79]

Thanks for your info , it really helps ,
Well I agree with you about the inrush current and there is two valves , The name plate says that it's 60 HZ and 120 V , so I think we are fine , but the problem is the the switching time is around 4 sec , so we have high inrush current , do u think that using time delay fuse 2.5 AMPS will help us ?? or do we have to think in another solution ???

Regards

F

 

[itsmoked]

Fernando79; has this installation ever worked or has this problem been always present?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com