Re-Assembly in a humid environment?

Discussion space for posts that don't fit into the other categories, such as issues with VideoRay products, or general ROV tips.

Re-Assembly in a humid environment?

Postby underseaservices » Fri Sep 17, 2010 11:53 am

Any advice on how to remove moisture from a VideoRay housing when re-assembling it in a humid environment? The average humidity here is over 70% almost year round. I remember reading somewhere that someone was using a gas (nitrogen?) to evacuate moisture during re-assembly. Any advice on this?
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Re: Re-Assembly in a humid environment?

Postby tom_glebas » Tue Sep 21, 2010 1:33 pm

Of course, assembling ROVs in a controlled environment is preferred, but in some cases this can not always be accomplished.

An air conditioned space is usually drier due to the condensation on the cooling coils. If you are in the field, and an air conditioned car or truck is available that would be preferred.

If a conditioned environment is not available, you can use this tip from Mike Underwood of Atlantas Marine in the UK (where he reports the high humidity is probably due to all the rain):

I set the ROV nose down with the rear dome removed , then power it up with lights on full and let it get hot for 10 mins before sealing it up. Its the only way I know that is good for the field (ie no special tools or gases).


Brett Kolb of VideoRay suggests this method:

One method is blowing compressed air in the hull and immediately installing the main dome. The air in the tank is dry and drops the moisture from around 35% down to 10-15%. For systems that are already assembled, we could remove the light cones and blow compressed air into the housing for about 30 – 60 seconds.


Tom
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Re: Re-Assembly in a humid environment?

Postby underseaservices » Thu Sep 23, 2010 6:22 am

Thanks Tom. The humidity level in our office ranges around 40-47% (while outside it's almost always 70%+). Would the humidity in our office (plus one of those silica gel packs secured inside the housing) be low enough?
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Re: Re-Assembly in a humid environment?

Postby tom_glebas » Thu Sep 23, 2010 9:41 pm

I think that if you add some extra desiccant packs, you should be okay even if you can start at say 40%. VideoRay sells desiccant packs, but they are also available from a variety of sources.

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Re: Re-Assembly in a humid environment?

Postby prowe » Tue Oct 05, 2010 9:54 pm

"Dry Nitrogen" is what I use. Displace the air and humidity with Dry Nitrogen then seal it up.

Starting with a DRY ROV warm up the housing a bit above air temp then displace All the air with Dry Nitrogen. A plastic bag large enough to hold the ROV makes a good chamber and you can see what you are doing. Purged the bag with ROV inside a couple of times, then seal the ROV up, press the dome into place and remove the ROV from the bag.
The big ROVs use a vaccum pump and dry nitrogen to dry out electronic and camera cans before going deep where it can get really cold.

For safety reasons be sure to read the MSDS for Nitrogen. This link is an MSDS example for Nitrogen.
http://www.vngas.com/pdf/g7.pdf
Other safety concerns; Don't do this procedure in a confined space, Outside in the open air is best.
Nitrogen displaces oxygen, has no smell, taste or oder.

Suggest you have the provider of your Nitrogen provide you with their product MSDS.


Be sure to request "Dry Nitrogen" when ordering.

A small tank goes a really long way, You will need a regulator to despense it safely.

There are other gases that can be used to reduce humidity, but Nitrogen is one of the less expensive, available, non conductive and stable gases.

This may not be the best solution for the field, but it hasn't failed me in the years I have used this method.

pr/.
Patrick Rowe
Midwest ROV LLC.
prowe@midwestrov.com
Ph: 414. 840. 3855
Fx: 920. 699. 2535
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