Use of BCD dump valves

[tlehman]

It's been a while since I took my OW training, but I don't recall discussion about the use of BCD dump valves. Lots of time on the use of the inflator, holding it up to let air out, etc. I realize my impression was that the dump valves were more of an emergency feature than one you might use on a regular basis. However, as I read more here about buoyancy, I see people referencing the use of valves to trim such as when in a horizontal position. I'd appreciate input from the more experienced divers here about whether and how they use these valves.

Thanks

Tom

 

[cool_hardware52]

It's been a while since I took my OW training, but I don't recall discussion about the use of BCD dump valves. Lots of time on the use of the inflator, holding it up to let air out, etc. I realize my impression was that the dump valves were more of an emergency feature than one you might use on a regular basis. However, as I read more here about buoyancy, I see people referencing the use of valves to trim such as when in a horizontal position. I'd appreciate input from the more experienced divers here about whether and how they use these valves.

Thanks

Tom

For those diving a BP&W the single string actuated OPV is typically located on the divers lower left. Pulling it *UP* moves the valve to where the gas is in the wing and allows dumping with out changing the horizontal or slight heads down trim.

One needs to be a bit careful when discussing "dump vales" and the use of "dump" valves simply because there are so many variants and people use the terms interchangeably.

Many consider a cable actuated "rapid exhaust" that is opened by extending the corrugated fill hose to be a "dump valve"

I try to keep things straight by referring to the valve on the lower left of most wings as the "OPV" and "rapid exhaust" type valves as dump or "rapid exhaust" to avoid confusion.

Tobin

 

[Bob DBF]

Depending where the air bubble is due to your trim, it may be easier to use the dump valve rather than changing your position to use the inflator / deflator. If it is not an emergency you don't just yank the valve completely open, you pull on it to let out just the air you need to lose. It takes time and use to get good at dumping the right amount, but practice makes perfect.



Bob
-----------------------------------------------
I think that advocating unsafe and dangerous practices is both stupid and foolish. That is why I don't tell people to do what I do. Dsix36

 

[miked]

The air inside your BCD/wing will "migrate" to the highest part of the wing, based on your body position. That is why you would lift the inflator hose to dump air-it places the outlet at the high point, providing that your body position is close to vertical-at least shoulders/head higher than your waist. Sometimes, you may have to shrug,or roll your shoulders to help move the air to that area of the BC
If your body position is closer to a horizontal one, one of the other dump valves could be at (or closer to) the highest point of the wing/BCD. As such, they would be the "easier" choice to use when dumping air.
If you are, for whatever reason, in a head down configuration, then your rear "butt dumps" would be at the highest point.

I use, and would suggest using, whichever is most convenient, based on body position, and of course where the dump valves are located on your gear. Their placement is not universal. (Some typical locations, but not all are on every BC: Hose dump; Shoulder hose pull dump; Dump valve on the shoulder that doesn't have the inflator hose; "butt dumps" left and or right side.)
As you get more experience, you'll probably find which one(s) you prefer to use.

One last thought: in open water, IMHO there is no shame in "going vertical" as needed, to use your hose dump to release air. Actually,If you are close to horizontal, you can still use the hose, but would have to lift it more, and possibly rotate or lift your shoulders.
If that is what you are most comfortable doing, do it! (I do at times)
Wishing you many years of safe diving.

Edited to ad: Damn, I am a slow typist. I agree with the other 2 posts!

 

[tlehman]

Depending where the air bubble is due to your trim, it may be easier to use the dump valve rather than changing your position to use the inflator / deflator. If it is not an emergency you don't just yank the valve completely open, you pull on it to let out just the air you need to lose. It takes time and use to get good at dumping the right amount, but practice makes perfect.

Bob

Thanks. I've got a small number of dives under my belt, but I have found it sometimes awkward to release some air without having to disrupt my dive to change positions a bit. I'm sure as my buoyancy skills improve, I'll have less need to do this. It sounds like these valves are designed to support periodic use. That was part of the question in my mind.

Appreciate also in the earlier post the heads up to the differentiation between exhaust and dump valves, but the difference is still not clear to me. Do they function in different ways? Are designed differently?

Given the variation, this might be another factor favoring purchasing rather than renting a BCD.

I'll practice this in future dives.

Tom

 

[cool_hardware52]

Thanks. I've got a small number of dives under my belt, but I have found it sometimes awkward to release some air without having to disrupt my dive to change positions a bit. I'm sure as my buoyancy skills improve, I'll have less need to do this. It sounds like these valves are designed to support periodic use. That was part of the question in my mind.

Appreciate also in the earlier post the heads up to the differentiation between exhaust and dump valves, but the difference is still not clear to me. Do they function in different ways? Are designed differently?

Given the variation, this might be another factor favoring purchasing rather than renting a BCD.

I'll practice this in future dives.

Tom

OPV and Rapid Exhaust.

Both release gas in your BC.

OPV's are Over Pressure Valves, i.e. spring poppets that will vent if the BC is fully filled, but can be actuated by pulling on a cord that protrudes from the center of the valve.

Rapid exhaust valves are typically fitted at the point where the corrugated fill hose joins the BC. They are actuated via cable inside the corrugated hose and connected to the power inflator. Yanking on the corrugated fill hose opens this valve that is between the divers shoulders.

Rapid exhaust valves are also often called "pull dumps" which leads to confusion because you also "pull" on the cord on an OPV to vent.

The most of the "tech" community prefers a plain elbow in place of the "rapid exhaust / pull dump" because they can stick open either because of an internal failure or the corrugated hose get caught on something. The internal cable can eventually saw it's way through the corrugated hose, and yanking on your bc / hose fitting is just not the best idea.

The typical "tech" style wing will allow the diver to vent via the OPV, or by raising the power inflator and pushing the oral inflate button.

Tobin

 

[kwinter]

Many BCDs, especially rentals and lower end models likely to be used by newbies, do not have an OPV/dump valve. So I wouldn't expect this to be discussed in OW class. The "rapid exhaust valve" aka pull dump, is an almost universal feature. So I would expect OW instruction to include something about pulling that in case of runaway buoyancy, but using the inflator release for fine buoyancy control.
And when I find myself quoting Tobin, then something must be terribly wrong.


iPhone. iTypo. iApologize.

 

[TSandM]

I wasn't taught anything about the fact that there were multiple places to release gas from my BC, when I took my OW class. We try very hard to encourage our students to use whichever exhaust point makes the most sense for the position they are in, and we also teach them that something they should check during their BWRAF is the position and function of all of the dumps/exhaust valves on their particular BC. They do vary.

I don't like pull dumps. One of the only ways you can disable a BC so that you can't put ANY air in it, is to pull the corrugated hose off the bladder. And yanking on it repeatedly is a great way to set yourself up to do that.

 

[dmoore19]

As for the terminology, when you talk about OPV is that also called a butt dump? If so, when horizontal that is the first place I go to dump air. When ascending I have dumped most of the air from my BC before I start the ascent. The inflator is for the fine tuning as I ascend or the initial dump when decending. I seldom pull on the corrogated hose and use that way to vent, I do know it's there for when I need it though.

 

[NorCalDM]

Bottom line no matter what you call them they are just valves to control the air volume in the air bladder which one you use to release air is going to depend on your orientation in the water and style of air bladder it is. I have one back inflate BC that has a U shape badder and it will trap air so I wil roll the air around to release it and I have a back plate with a donut style bladder that is easy to release air just use to one that is at the highest point at the time. The more you dive and dial in your weighting the less you will need to use your BC to adjust your buoyancy.