| Author | Message | ||
     Brian Vogel Grand Master Username: guyslp Post Number: 624 Registered: 6-2009 |
Hello All, Yanked the ACV & accumulator off of the car yesterday and am doing some first-time charging with my mini setup. The accumulator was completely discharged and the secondary seal, a PTFE sphere placed in the charge port hole, was quite thoroughly crushed by the port cap when it was tightened on the last time. The diaphragm is clearly not ruptured since I am able to pump the thing full of nitrogen with my "paint ball tank charging kit" and it doesn't escape out the top as I'm doing so. After charging, though, the leakage from the primary ball bearing seal is quite noticeable. You can hear it hissing for a while, and if you let the hissing stop the accumulator is not completely discharged, but will emit a pronounced hiss of gas if one pushes down on the ball bearing to release it. What I can't determine is if this is a feature, such that the seal doesn't seat if you overcharge until the gas pressure is down to about 1000 PSI (although the built-in regulator on this tank is supposed to stop right around that figure). If necessary I will tear the accumulator itself apart and do whatever is necessary as far as cleaning the seat or using a substitute ball bearing. I'm just not sure what's necessary since the above could be "normal" behavior that necessitated the secondary seal. This time I plan on putting in a tertiary seal in the form of a small EPDM O-ring in the base of the charge port cap. When I do this and just firmly screw the cap back on by hand I don't seem to have a leak. If I leave everything off the thing will completely discharge in a fairly short period of time. Experiences regarding what I should, or should not, be hearing as far as gas escape would be appreciated. Brian | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 311 Registered: 5-2012 |
Brian I personally would dismantle the sphere and at the very minimum replace the steel ball. As you are aware, a small escape of gas is expected when the charging line is disconnected so I am presuming the escape of gas is excessive, which would indicate the valve seat is not perfect. When I reconditioned my spheres with a kit from FS they had replaced the ball with a pin carrying a small O-ring. This was very effective and resulted in zero identifiable gas loss on disconnection of the charging line. When you rebuilt your spheres did you use a new diaphragm? I ask this as I have read they become porous to high pressure nitrogen at the molecular level and leakage will increase as the diaphragms become older, hence the recommendation to change diaphragms even if they look in good condition. Unfortunately it does not appear that FS sell the replacement valves individually, but only as part of a kit that includes a new diaphragm, hence my question as to whether the diaphragm should be replaced as well. I do realise the rapidity of the gas loss would not be down to a porous diaphragm, just that if it should be replaced it is a good reason to justify the cost of the reconditioning kit that contains the superior valve. Geoff | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 626 Registered: 6-2009 |
Geoff, I now believe I may have an explanation for the (relatively) rapid depletion on this accumulator. When I took off the charge port cap there was no O-ring at the bottom, which should be there as the tertiary seal. I had the accumulators charged elsewhere and I may have accidentally forgotten to send the O-ring along or it could have been omitted unintentionally. Both spheres had their diaphragms replaced as part of their overhaul. I've seen the Flying Spares Accumulator Rebuild Kit and I have to say that their primary sealing valve design is vastly superior to the original. Unfortunately, the kit I had was not from Flying Spares. I'm having my friend the aircraft mechanic recharge the sphere tomorrow, to slightly above 1000 PSI, and with all three seals in place to prevent the gas from escaping. Let's hope "the system" works this time. Brian, who had the ACV/accumulator assembly out of the car in less than 30 minutes this time - having a lift is very handy that way (as is having practiced this multiple times now) |
