2 Flow meters and 1 Draeger question

[ancl]

This might sound like a stupid question but here goes.....

Just doing the flow rate checks on my Dolphin ( brought second hand, training done last month, and finally got a pass out from wife / work to go for a dive this morning )

I was supplied with two flow meters with markings for 32/40% on one and 50/60% on the other in the purchase.

If I set up the valve to use the 32 or 40% jet and attach the flowmeter for 32/40, the floating ball seems to be read just over the mark for 32/40 - ok I think this is okay, its not sitting at the bottom or at the top of the meter.

*but* if I set up the valve to use the 50 or 60% nozzle, and plug in the meter for 50/60% as soon as I open the valve the meter indicator ( little ball ) goes way high, almost coming out of the top of the meter, I've just checked on the 40% nozzle with the 50/60 meter and get the same results, 50/60 nozzles on the 32/40 meter and the reading is about half way up the meter, not pushing the ball out the top of the meter.

I sort of get the feeling the 50/60 flow meter has gone faulty, does it sound like this to anyone ?

Andy

[Neil McLeod]

Firstly I am not an expert having only dived on the Dolphin for a season but I do use pressure regulators and rotometers everyday at work.

Are you using the appropriate gas mixes in each case (32, 40, 50, 60)? Each will have a slightly different density, viscosity and constants for sonic flow.

Secondly, is the bobbin in the 50/60 flow meter going to the top and sitting there or is it flicking up and down - pulsing?

It might be the flow meter. These are variable orifice flowmeters. The internal channel that the bobbin sits in is tapered, getting wider towards the top. The meter must be vertical and the bobbin should not be touching the sides when floating. If there is any dirt inside the tube this will effectively narrow the diameter and force the bobbin higher for any given flow. A leak proximally to the bobbin will obviously cause it to underread. So provided it is clean, has the correct bobbin and gas mix and is used vertically there is nothing to go wrong with one of these. (The bobbin settles when the forces up & down are balanced. The downwards force is the mass of the bobbin x G. The upwards force is the nett pressure difference across the bobbin / its surface area.)

You can push a flow too high if interstage pressure (IP) is too high. If so, and 32/40 reading is about right then consider a problem with the sonic valves. the IP should be checked using 100 bar supply of 50%.

In short if you don't have the test equipment, take it to get IP and flows checked on independant meters. Something is wrong and unless you are happy to monitor the PPO2 very closely, you should not dive a unit which isn't coming in on spec.

I too have had a similar problem which was down to the IP needing adjusted. Beaver sell a simple IP meter for about £15.

Not much help I know but hope it gives you something to work from.

Neil

[narked at 90]

hi Andy are they allowing you to dive again?if you don't have an I.P gauge bring it unit over to me in Kettering and I'll give it the once over for youthere is very little to go wrong with the flow meters but it's worth a second check, i would suspect a flow problem or IP problem.the dolphin first stage has an in build safety feature that creeps the IP up if you get a blockage in the jets, there are 2 jets in every holder, so if you have a blockage in one of these this could be another to trigger the rise in IP which would increase the flow on the other jet,this may all be wrong but i suspect you have a problem in serious need of attention

[ancl]

Neil - thanks for the information

John - Been cleared to dive for some time now, thought you knew that I left Higham Ferrers in March 2005 to start a new life in Netherlands, been here about seven months now and managed to aquire a Draeger second hand over here.

Interesting comments about the IP.

The ball on the 60/50 flow meter sits right at the top of the meter, no pulsing.

Took the unit to Oostvorne this morning for a test dive, using EAN50 on the 40% nozzle, spent ages trying to descend with no joy, adding weight, eventually using a leg on a jetty to get down to about 3m, whilst exhaling through the nose as taught on the course, as soon as I hit 3m I started to come up again, the best way to describe it as if the counter lungs are filling rapidly, after several attempts I aborted the dive.

Had planned to go onto the 50% jet to test, as I had done my training on the 50% jet.

I've got two thoughts here on what might be going on.

1) The bypass has stuck open so its continually adding gas into the loop

2) Since reading the replies, maybe the IP is too high forcing the gas into the loop ?

Maybe they are one and the same thing.

I did plan to test the 50% jet, but found I was out of gas and called it a day.

Whats changed since the course and this dive ? I got the rebreather serviced locally, so will drop the guy an email tomorrow asking whether he can check the jets / IP for me.

Really feel like someone is telling me to give up this diving lark !

[narked at 90]

hi andy i new you were thinking of moving to the south of england! but not to the cold old neither regens, hope it's going well over there.
the ip should be around 16.7bar, very high compared to over 1st stages
if it's to high to could push past the bypass....i asume opv vents on every breath?
are you using monitoring?
kind regard john routley

Originally Posted by ancl

Neil - thanks for the information

John - Been cleared to dive for some time now, thought you knew that I left Higham Ferrers in March 2005 to start a new life in Netherlands, been here about seven months now and managed to aquire a Draeger second hand over here.

Interesting comments about the IP.

The ball on the 60/50 flow meter sits right at the top of the meter, no pulsing.

Took the unit to Oostvorne this morning for a test dive, using EAN50 on the 40% nozzle, spent ages trying to descend with no joy, adding weight, eventually using a leg on a jetty to get down to about 3m, whilst exhaling through the nose as taught on the course, as soon as I hit 3m I started to come up again, the best way to describe it as if the counter lungs are filling rapidly, after several attempts I aborted the dive.

Had planned to go onto the 50% jet to test, as I had done my training on the 50% jet.

I've got two thoughts here on what might be going on.

1) The bypass has stuck open so its continually adding gas into the loop

2) Since reading the replies, maybe the IP is too high forcing the gas into the loop ?

Maybe they are one and the same thing.

I did plan to test the 50% jet, but found I was out of gas and called it a day.

Whats changed since the course and this dive ? I got the rebreather serviced locally, so will drop the guy an email tomorrow asking whether he can check the jets / IP for me.

Really feel like someone is telling me to give up this diving lark !

[ancl]

John

I'm using the Air Z / Oxy2 for monitoring, the OPV seems to be constantly firing, turned the gas on and the lungs filled very quickly, looks like an O-ring is about to fail as well as I just put the rebreather in the bath ( wife is going to freak when she see's the bathroom is full of rebreather bits and bubbles are flowing from one of the hoses entering into the first stage.

Well it never rains it pours.

[narked at 90]

sound to me that you should not be diving this unit and take it back to the guy that serviced it and get your money back!!
john

[ancl]

John

I've sent an email to the guy, so just a case of waiting for a reply.

Hows life over in Kettering ? Club-sub still going ? Brendan still about ?

[narked at 90]

havent talked to brendan in a long time.....waster!
and club sub are usles so dont give them any money and now all my time is spent on my new buisness www.narkedat90.com so dont go out any more.....sad old life!
john

Originally Posted by ancl

John

I've sent an email to the guy, so just a case of waiting for a reply.

Hows life over in Kettering ? Club-sub still going ? Brendan still about ?

[ancl]

Got it confirmed that the flow rate was too high after watching the Draeger flow bag fill up within 90 seconds, where the book said 3minutes !

Dropped the unit in to be adjusted while I wait, slight adjustment, flow meter check by myself - normal flow rates resumed !

Want to go diving now but got family visiting - doh !