| Scubapro Manifold Fettling
I'm not sure if this is the correct forum for something like this, there doesn't appear to be an area for Maintenence/DIY. Maybe an Admin could shift it to somewhere more appropriate if necessary....
As some of you will know, I'm a great fan of MDE manifolds due in no small part to their bombproof build and the ease with which the valves turn, even when the tanks are full.
Sadly, I no longer own a 12 litre twinset with MDE valves. The two I have currently are equipped with Scubapro and Agir-Brokk valves which, although gaining admiring glances from the guys in black, are a bugger to turn especially at high pressure.
When I first took ownership of the Scubapro manifold it clearly needed some TLC. So I stripped it down and gave it good clean & degrease followed by a soak in vinegar and an ultrasonic ‘jacuzzi’.
I reassembled the now shiny parts using Krytox grease and all seemed well, until I had the tanks filled. They were marginally better, but still unacceptable.
So, after using the gas, I stripped each valve again and made sure every surface was coated with grease. Again, a little better but not up to the high standard I was used to with MDE.
They were much easier to turn at low pressure than at high, indicating that they weren’t balancing very well. I’d noticed before that the threaded brass seat has a hole in the back (knob side) which I thought was there to assist balancing, but there doesn’t appear to be a matching hole on the other (cylinder) side. The balancing seems to take place by gas migrating through the thread which obviously takes some time.
Yesterday, I decided to take some serious action.
I stripped each valve down and gave everything a good clean up. I then took a junior hacksaw and cut a groove lengthways along the thread of the seat to a depth of about 0.5mm below the thread core. I cleaned up each thread using a needle file to remove any burrs (metal burrs and high-pressure oxygen are not good together!) and gave the thing another good clean and degrease.
After reassembling with a good coat of Krytox, everything was spinning freely, although I did notice things stiffening up when I screwed the knob back on. I noticed that, unlike the MDE valves, there’s no little Teflon washer between the valve & knob and under the pressure of the spring, there’s a lot of friction between the two metal faces. Whether Scubapro don’t use the Teflon washers or mine were just missing I know not, but I temporarily robbed some from other valves and used those.
This made a lot of difference and now things are much better, but I haven’t had the opportunity to get the tanks filled properly yet. I decanted some gas from another cylinder and at 20 Bar or so they still feel fine, but I won’t be able to get them filled up until Friday.
I’m guessing the gas should balance a lot quicker across the seat now, but if not, I can repeat the exercise with a full-size hacksaw to get a slightly wider groove.
If this proves successful, I’ll perform the same operation on the Agir manifold.
I’m guessing that most of this won’t make a lot of sense to those without an understanding of the inner workings of a pillar valve. I’ve had a quick trawl around the net for a schematic or cutaway diagram without any luck. Maybe someone else (Woz?) could post a link to one.
Now I need to track down some of those Teflon washers…… |