View Full Version : Does my manifold work properly?
alexmaclennan
11-03-07, 20:25
I've got a secondhand set of manifolded 300 bar 7s which I am playing with just now. I'm new to twinsets.
I always assumed that with a manifolded twinset you needed to shut down both one tank pillar valve and the manifold centre valve to isolate either first stage. In other words, I assumed that both the tank that the first stage is mounted upon and the other tank via the manifold fed the first stage independantly.
With my rig, I only need to shut down the pillar valve of the tank that the first stage is mounted upon to stop air going through the first stage. This means that the tank pillar valve also shuts off the air coming in from the manifold.
So it seems to me that the manifold is there to balance the tanks air pressure as you consume air, but you do not need to shut down the manifold as shutting either pillar valve has the same effect ie isolating the tanks and also shuts down one first stage.
So why does the manifold have a valve? In case through choice you want to dive with indie 7s?
Am I missing something?
alex
pretty sure its easier to show people than write about it....
how a manifold should work.....
lets call them tank A & tank B, reg A & reg B for clarification.
open all 3 valves, pressure to both gauges.
breathe from either reg, both cylinders drain at the same rate.
close centre valve on manifold, breathe from A will use that air, breathe from B will use that air.
opening the centre valve will balance the air pressure equally between A & B tanks.
close manifold valve, close tank A pillar valve, re-open manifold valve.
this will allow you to breathe both tank A & B air which will be of equal pressure from regulator B only.
reg A will have no supply.
close manifold valve, close tank B pillar valve, re-open manifold valve.
this will allow you to breathe both tank A & B air which will be of equal pressure from regulator A only.
reg B will have no supply.
Lizardland
12-03-07, 00:45
Hi Alex,
both 1st stages have access simultaneously to both tanks.
Shut one pillar valve down and the opposite 1st stage still has access to the air in both tanks.
Shut down the isolator valve and the left 1st stage has access only to the left tank and the right 1st stage accesses only the right tank.
The way I dive a manifold (simplified version) is if I have a problem with a reg that I can see e.g. the 2nd stage is freeflowing, then I shut down the respective pillar valve. If I have a problem that I can't see but know I'm losing air then I close the manifold.
Think of the pillar valves as off/on switches. The isolator valve controls whether you have independant or joined cylinders.
I rig my twinset so that all my main bits of kit i.e. the reg I breathe off of and my bcd, are run off the right side. The secondary stuff i.e. backup reg, drysuit and SPG, run off the left.
If in doubt, go for the isolator. Worst case, you'll lose half your air but you'll still have the other half. If you shut down the wrong pillar valve then you lose the lot.
I don't know if it is especially clear in this photo but it's the best that I've got that shows my twinset rigged:
http://www.lizardland.co.uk/francejun2004/day-4/four-11.jpg
Yellow hose is my primary, wing crosses behind my neck. Backup reg is on a loop of bungee round my neck. If there is a problem then I donate the reg which is in my mouth (it's on a 2m hose).
Cheers,
Stuart
so what you guys are saying is that when you close the cylinders pillar valve, you only shut the air off to it's respective regulator?
alexmaclennan
12-03-07, 10:16
Thanks to Stewart & Stuart,
I understand all that Stuart has said. I have rigged my twinset hoses - although inverted - in the same way. I also have heard the 'isolate valve if you know which valve the problem lies' with, versus 'turn off manifold if you do not' piece of advice.
Stewart (maybe you should both be known as Bruce?), I did not know about this piece of valve sequencing:
close manifold valve, close tank A pillar valve, re-open manifold valve.
this will allow you to breathe both tank A & B air which will be of equal pressure from regulator B only.
reg A will have no supply.
close manifold valve, close tank B pillar valve, re-open manifold valve.
this will allow you to breathe both tank A & B air which will be of equal pressure from regulator A only.
reg B will have no supply.
I wonder how this bit of plumbing works?. I'll try it and get back to you.
alex
Scuba-Doh!
12-03-07, 11:05
Might this help?
http://en.wikipedia.org/wiki/Manifold_(scuba)
http://upload.wikimedia.org/wikipedia/en/thumb/3/37/Manifold_scuba.jpg/180px-Manifold_scuba.jpg
so what you guys are saying is that when you close the cylinders pillar valve, you only shut the air off to it's respective regulator?
....yes....
...why?...
look at SD's pic above.
if you closed the left valve the air cannot pass it to feed the reg.
the air can still pass under it along the manifold to the next cylinder.
look at SD's pic above.
if you closed the left valve the air cannot pass it to feed the reg.
the air can still pass under it along the manifold to the next cylinder.
Not the Why I was asking.
But having thought about it, I've just made myslef to look like an idiot!
Note to me: Must engage brain more often...
alexmaclennan
13-03-07, 09:20
pretty sure its easier to show people than write about it....
how a manifold should work.....
lets call them tank A & tank B, reg A & reg B for clarification.
open all 3 valves, pressure to both gauges.
breathe from either reg, both cylinders drain at the same rate.
close centre valve on manifold, breathe from A will use that air, breathe from B will use that air.
opening the centre valve will balance the air pressure equally between A & B tanks.
close manifold valve, close tank A pillar valve, re-open manifold valve.
this will allow you to breathe both tank A & B air which will be of equal pressure from regulator B only.
reg A will have no supply.
close manifold valve, close tank B pillar valve, re-open manifold valve.
this will allow you to breathe both tank A & B air which will be of equal pressure from regulator A only.
reg B will have no supply.
OK Stewart, thanks for the idiots guide. It works just like you said. I've tested it in various valves off and on combos, purging 40 bar and looking at gauges once valves re opened. Happy bunny once more,
alex
Not the Why I was asking.
But having thought about it, I've just made myslef to look like an idiot!
Note to me: Must engage brain more often...
what 'why' were we wondering? :D
Alex,
take them in the pool & practice some shut-down drills.
its much easier to do them there, bit more difficult to reach them with a drysuit on.
safety quetion...open to everyone.
what would you do if the centre manifold started leaking air? :eek:
Lizardland
13-03-07, 21:04
what would you do if the centre manifold started leaking air? :eek:
Shut down the isolator, switch to the reg which is attached to the leaking side and breathe it down.
If it is the actual isolator valve which was leaking then I'd still do the same, in case only one side is affected. The valve itself failing is the only way that you'd be at risk of losing all your gas. I've never heard of this happening. For something that's designed to take 300bar+ then it would need some serious damage.
Usually with manifolds where you get problems is where the crossover bar connects to the pillar valve on the cylinder. Closing the isolator will save at least 1/2 your gas. Apeks manifolds are very prone to this as they are not as strong as MDE. Another big cause of leaks in manifolds is completely draining the set e.g. dumping a leftover trimix fill so you can have a nitrox fill. It's always best to leave a couple of bar in a twinset to keep all the seals under pressure.
Cheers,
Stuart
alexmaclennan
13-03-07, 21:45
I assume you can hear it leaking and your buddy should hear or see it too. You will not know it is the manifold that is leaking - it could be a hose or O ring.
Quickly review (seconds only):
Q How deep are you?
Q Any deco penalty?
Q Any issue about being in an overhead/ restricted environment or need to get back to where you can safely ascend?
Q How much air do you have left?
Q Do you have a side slung bottle or is a bottle at a 5m deco station?
1. Signal to your buddy to stay close and start making a controlled ascent. Speed of ascent has been debated before.
2. Turn off manifold valve - to try and conserve at least half your air
3. Turn off Right pillar valve (change to breathe thru alt reg) and breathe down or purge main reg.
If bubbling does not stop, continue ascending and prepare to use your buddy's alternate air or your side slung if you are in the right depth.
4. Turn on Right Pillar Valve - purge main reg to check valve open
5. Turn off Left Pillar valve (change to breathe thru main reg) and breathe down or purge alt reg
If bubbling does not stop, continue ascending and prepare to use your buddy's alternate air or your side slung if you are in the right depth. At this point you know you are going to lose all your gas as you've isolated the tanks with the manifold valve and in sequence shut down both the pillar valves but you still have a leak.
6. If the manifold valve itself is faulty or leaking, you cannot conserve your air. If the manifold valve works then you can isolate the two tanks. You might lose all the air from one tank if the joint between manifold and tank is leaking, but your pillar valve shutdown procedure should work out which side is at fault.
What have I forgot? Perhaps to dive indie cylinders? Risk of manifold failure and difficulty in isolating the manifold are the two reasons commonly given for diving indie cylinders.
alex
complicated stuff! :eek:
Perhaps to dive indie cylinders? Risk of manifold failure and difficulty in isolating the manifold are the two reasons commonly given for diving indie cylinders.
I guess though if you have a free-flowing reg with manifolded twins, you can shut it off & not lose the whole tank as may happen with indies.
Lizardland
14-03-07, 01:35
1. Signal to your buddy to stay close and start making a controlled ascent. Speed of ascent has been debated before.
I'd sort my gas out before I started the ascent. I don't trust my buoyancy control enough to be able to be in control of my ascent and be sorting out the leak, doing valve drills, etc. Too much going on at once for me.
Worst case is that you have to do a shared ascent. Second worst is that you lose half your gas. Neither should be a problem if you've planned your gas margins right. Losing control of your buoyancy whilst trying to sort out the leak is pretty major.
It's all a trade off. Indies mean that you have to stay on top of keeping your bottles balanced, knowing which SPG you should be looking and complicates gas sharing but you will always have half your gas supply intact (unless you get the first two things wrong). A manifold means less monitoring, no need to swap regs, potentially more gas in an emergency (or at least more options to manage it) and simpler gas sharing but you pay the price by being dependant on the manifold a. doing it's job and b. you being able to do your job and work the manifold the right way.
Cheers,
Stuart