nh3 and water

[ART KUHN]

Hello people,

for servicework i sometimes empty parts of an installation by letting the gas flow throug water with a checkvalve in the hose to avoid the water from being sucked in the installation.I know this sometimes happens but i have no idea why and when it is most litely to happen

Can any one tell me??

Kind regards Art

[nh3wizard]

It happens when whatever you are pumping down pulls it self into a vacuum, Ive seen it happen on separators on compressors when the bypass line is left open.

[US Iceman]

Hi Art,

Welcome to the RE forums.

There are a couple of possibilities. The primary mechanism for what you are describing is a differential pressure.

If the internal system pressure is lower than the atmospheric pressure, the water would be pushed into the system. In other words, if a slight vacuum exists in the system, the atmospheric pressure is higher than the internal pressure of the system. Therefore, the water would be pushed into the systems.

The check valve is used to reduce the possibility of water flowing back up the hose and into the system.

A similar thing happens when oil pots are being drained. If the oil pot is not isolated from the system (during oil pot draining) air can rush back into the system (if the system is in a vacuum).

A secondary effect of water migration is due to the hygroscopic nature of ammonia. Remember, one of the terms used to describe refrigerant grade ammonia is "Anhydrous", which means "without water".

Ammonia is very dry and absorbs water very well. So even if there were no pressure difference between an open hose (to the system) and a bucket of water, the water would still travel to the ammonia.

The purpose of using the bucket of water is to absorb the trace ammonia gas, so the area does not stink when you perform this operation. As you have probably discovered, the water begins to stink after a short period. This means the water is becoming saturated with ammonia and cannot hold more ammonia. At least not enough to keep the smell down!

[ART KUHN]

Hi usiceman and nh3 wizzard

I understand that the water absorbs the smell and warms up because of it.For example:a compressor with the sevice valves closed and the pressures are equelised up to 5 bar when i let go of the amonia in a bucket with water i stil have to be carefull that the water doesnot go in to the compressor.Since the pressure is not below 0 bar it must be because of the hygroscopic nature of amonia.

please correct me if i'm wrong

kind regards Art

[US Iceman]

Hi Art,

The cause of the of the water warming up when absorbing the ammonia is due to an "exothermic reaction".

In thermodynamics, the word exothermic describes a process or reaction that releases energy in the form of heat.

The way I have always looked at the problem you describe is; as long as the ammonia pressure is higher than the pressure at the open end of the hose, the ammonia will flow out and the water does not travel backup up the hose.

The water would only be absorbed (by the hygroscopic nature) when the pressures are equalized.

That's my opinion.

[NH3LVR]

Glad to have you aboard, Art.
I think there may be more to it than that, although I do not have a scientific explanation.
I learned many years ago that the easiest way to get water into a NH3 system was to hook a hose to it, leave it in a bucket of water, and walk away. Opening a few compressor crankcases and cleaning them out cured me of that.
I often will hook a vacuum pump up to a system after I get it down to atmospheric, putting the discharge under water. If I do not use a check valve in the outlet of the pump a strange thing occurs. The NH3 touches the water and makes a crackling noise (like we expect). Then the water flows back up the hose into the pump and the whole cycle repeats itself. You can watch the Water flow up and down the hose if it is clear. I always thought that the gas expanded and then contracted quickly, like an explosion.
Hard on Vacuum pumps.
But I will not bet any thing of value on my theory.

[ART KUHN]

thanks nh3lover that's exactly what i mean

I do the same with the vacuumpomp for example on a 1/2'' sevice vale on the hp from the compressor but then i open the oil outlet in the cranc case to get an air flow throug the oil and the compressor so it's easyer to get the amonia out.

Regards to all and thanx ART