why would a check valve be necessary?

[USAeng]

All 1/2" steel piping with #2 fuel oil flowing

There is an actuated shutoff valve then about a 20' run of pipe then a 10' drop and another 8' run to an oil gun with tip out in the furnace

There is a negative pressure coming from the furnace, and there is a small additional negative pressure created during a 30 second purge with the oil off and air still on... probably equals about 3 psi total...

So why would there need to be a check valve installed immediately before the oil gun?

Whouldnt the pressure after the valve be 0 and the pressure from the atmosphere be like 15-3 = 12psi + friction and such... so the oil would all stay in the line except for maybe a little that would come out that was in around that last 8' run?

I think a check valve would do little to almost nothing here... a couple people are insisting that there HAS to be a check valve there... am I missing something?

Thanks for any thoughts

 

[SeanB]

Is there anything else going to the oil gun - say maybe steam?

 

[BigInch]

For one thing it will keep air that replaces the oil that has run out the end of the pipe from making its way back to wherever it can make its way back to.

"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com

 

[Compositepro]

The primary purpose of the check valve may be to introduce a forward pressure drop (cracking pressure to open the spring) and therefore prevent the oil lines from draining into the furnace when it is shutdown.

 

[kacarrol]

One project I worked on some of the engineers said that they wanted the oil pipe line to retain the oil which would prevent corrosion. Maybe the same case here?

 

[pipesnpumps]

It is most likely to prevent the atomization air (compressed air) from backing up through the burner nozzle. Fuel oil and compressed air connections will be near the windbox, and these go to the oil gun which uses the pressurized air to atomize the oil.

I am not familiar with the specifics of how oil burner guns are configured, but it seems possible that the air could backup through the oil line if the oil pump was suddenly shut off or a valve closed.

 

[Latexman]

or the gun got plugged with wax in cold weather

Good luck,
Latexman

 

[USAeng]

Ok... so I guess the air could get up into the line causing the line to leak out... I was thinking that the pressure on the bottom would hold in the oil like putting your finger on a straw... 0 on top and atmosphere on the bottom...

anyone know a good check valve manufacturer that would sell one that's threaded to insert into this kind of line?

 

[DLite30]

Swagelok

 

[USAeng]

Ok... I guess I still dont understand the basics here... but thank you very much for the help so far...

After the shutoff valve there will be 0 psi, at the furnace the pipe has an atomizer tip on it that is open to the atmosphere 14.7psi... so lets say there is only 2psi of static pressure in the pipe... the friction and fittings would equal that and you are then left with 14.7 atmospheric pressure from out in the furnace holding the oil back in the piping...

there is no air in the line only pressurized oil... air is injected at the very end of the gun for atomization.

If someone can explain how this will work using some fluid mechanics fundamentals... that would really help me I think.