why does a check valve not work as a vent during filling

[saumian]

We have a 5000 US gal tank for aqua ammonia storage. In addition to inlet and outlet( these two are closed most of the time) a 2" PVC with a ball check valve is connected at the top of tank as a vent. We utilize this 5000 gal ammonia over a period of 5 months without loosing any ammonia. However, it takes only 30 minutes to refill this tank from bulk trailer, and onone wants to stay inside the facility due to ammonia smell. Why the check valve with PVC vent is not functioning as a vent during this fill up? Should we have to have additional-independent vent( with regular ball valve) in addition to the one we have so that we can manually keep it open and close only for fillup purpose?

 

[pennpoint]

saumian
It appears to me that the check valve spring is too strong and will not allow the seal plate/ball to lift. It also appears to me that the venting is occuring at the fill port. Do you seal the fill port when filling? Vapor will take the path of least resistance.
Maybe you could add a ball valve that would only be used during filling.
Try removing the spring in the check valve at next filling and see if it opens. If it a ball check and oriented in a vertical line you may not need the spring.
A new thought is the ball check there to pervent a vacuum or an overpressure situation. Which direction is its flow arrow. I should have asked this first!

pennpoint

 

[chicopee]

About installing a return vapor line back to the tanker in order to minimize fugitive emission during fill ups.

 

[saumian]

Pennpoint,

The check valve, we have, is a ball check valve, and it is oriented in vertical line. The direction of its flow arrow is upwards towards sky. Therefore, it will definitely help for overpressure situations.

Chicopee,

In fact we have two 5000 US gal tanks. One is for FRESH and the other is for SPENT. The bulk trailer brings fresh in, and takes the spent back. Thersfore, if we use return vapour line, then we will end up keeping the ammonia vapour in our spent tank everytime we fill up the fresh. This is one of the options which I am thinking about.

Saumian

 

[rbcoulter]

I am surprised you are using a ball check valve in pipe as a vent for the tank(s). A conservation vent is usually used for such applications.

 

[abcmex]

The situation is probably as follows:
when you use your aqua amonia and when you take liquid out, it fills with amonia gas evaporated by the vacuum you created.
when you fills probably the pressure of the tank increases making a release.
My first word of caution: check that the tanks can resist the vacuum created when emptying, I already have seen some colapsed tanks.
The second: check that the pressure created by the check valve during the unloading is lower than what the vessel can resist.
Even better than this: use a properly designed and constructed conservation vent (like Protego). A check valve has not a very exact release pressure.

if you can not return the Amonia vapors to the delivery truck they can be easily captured with water (scrubber).
Rgs

 

[saumian]

Rbcoulter,

I believe that you mean that A conservation vent should have been used as the breather, not as an apparatus which can get rid of the ammonia vapours in our situation. Do We need an exhaust even with a conservation vent(valve)?

Saumian

 

[micjk]

As rbcoulter says, a conservation vent is your best bet. you could then pipe this to your scrubber system, I'm certain you have such a system, thus eliminating release of ammonia vapors to the atmosphere.

Roy Gariepy
Maintenance and Reliability Dept.
Bayer Corporation Dorlastan Fibers Div.
Goose Creek, South Carolina USA

 

[lilliput1]

A vent line should have no valve on it but some process require vent filter. The check valve is usually used as a vacuum breaker to let in air if the tank is under vacuum to prevent it from raspturing. However if the tank is properly vented there would be no need for a vacuum breaker.

 

[rbcoulter]

Conservation vents are the typical devices one uses to control emissions from storage tanks. They are weighted and usually rated ounces/sq. in. because most atmospheric storage tanks cannot handle much pressure. The weights minimize the "breathing" loss that occurs when the tank temperature changes. Many times a backup emergency vent is installed in case the main conservation vents plugs.
Many facilities exchange the vapor with the supply tank truck to minimize venting losses. The conservation vent is the vent. If you have a vent and a conservation vent then the conservation vent function is defeated.

I suggest you contact a reputable supplier of conservation vents.

 

[abcmex]

There are several devices that work as conservation vent and there are several purposes that can be served. The main objective is to keep a controlled pressure inside a tank or vessel.
The conservation vent can release the overpressure to the atmosphere (if this is allowed, safe or enviromentally sound) or to a pipe for further treatment. in other cases (vacuum) to suck air from the atmosphere or from other systems.
As rbcoulter mentioned there are valves that have something like a big plate and a defined weight for each application. they can be configured to open by pressure or vacuum or both.
A variation of this exists with a membrane that is loaded by a liquid.
Other systems (older) uses a pipe that is dip in a liquid at a defined height, this requires a lot of work to keep the liquid level (usually water).
You can find futher information and profesional advice by companies like protego (

http://www.protego.com)

or protectoseal (

http://www.protectoseal.com/pvcvents.html)

Kind regards

 

[saumian]

Thanks for all for your opinions.

It appears that the check valve is there, in the original design, for over-pressure situations. The logic is there since a tanker truck with air-compressor have been used to tranfer aqua ammonia from tanker to FRESH tank.

It also appears that if we use a transfer pump to transfer AA from tanker to FRESH tank, then we may not end up having this much ammonia smell. A tranfer pump along with vapour return line would have fixed most of our concern.

We shall really need a check valve in addition to the Coservation valve if we have one, in case this Conservation valve fails.

Therefore, we now need a system with ducts, a pump, a cleaner ( scrubber) for fill up purpose of FRESH tank, to get rid of ammonia vapours in addition to the check valve system.

Thanks for all again.

Saumian