IP adjustment question

[halocline]

Is there a way to stop an excessive IP fall (25psi) on purging, or is it inherent in the design of the reg. I have 2 balanced diaphragm regs (different models from the same manufacturer) on 1 there is hardly any drop <5 psi on full purge, while on the other there is this excessive drop, which does make taking a slow breath harder, a big suck of air is OK on both. The bad one has been in for a service and still manifests this huge IP drop. The only adjustment I can think of that could alter this is to back off the tension on the spring closing the HP seat, but have not seen this referred to in any service manual, for any make of reg.
I hope one of the regulator guru's has some advice on this.

You need to check the IP drop with the same 2nd stage, are you doing that?

I have found some strange results comparing IP drop in different 1st stages. I came to the conclusion that some of the readings were affected by venturi effect in the port that the IP gauge was connected to. Ideally you'd have an IP gauge not connected to the LP inflator hose, but inline at the 2nd stage hose connection. This is all speculation, BTW.

I understand your concern about IP drop as a performance indicator; in a closed system, flow is proportional to pressure, so lower IP theoretically means lower flow in an otherwise identical set up. I just don't think you're likely measuring it accurately unless you have an inline gauge and probably one that's far above the typical quality of the gauges we DIYers use. Those are designed to measure static pressure, not dynamic, so they work well when there's no air flowing.

If you're really interested, you could invest in a flowmeter, maybe made by Dwyer, and then figure out a way to install that inline. Then you could directly measure the flow.

Interestingly, I did find a strong direct correlation between IP drop and performance in two doublehose regs, with the IP gauge connected at the hookah port. The DA aquamaster nozzle had a big drop and sluggish recovery, which translated directly to reduced flow while breathing hard at any sort of depth. The Royal aquamaster nozzle on the same reg resulted in a much smaller drop, quicker recovery, and noticeably better flow.

 

[LeadTurn_SD]

Thanks LeadTurn I change the second stages over so I've kept that as a constant only the first is on trial. My VX10 is around 15 years old and has served me well, as you say I think it is truly a top end reg, but recently I thought I'd get the latest top of the range reg by the same manufacturer. When it breathed like a dog I initially put it down to the miniature 2nd stage that it came with, and switched to a normal size 2nd stage, still it was not as good as the old VX10, that's when I started measuring pressures to try and understand why a top of the range reg performed badly. In most service manuals they say check the filter, the hose etc for a restriction to airflow, but I figure there has to be another less obvious solution like changing spring tensions. The art of reg tuning?? It's not mentioned in Vance Harlows book either.

It is possible the first stage may just be a "dog". Assuming proper assembly and lubrication, no problems with the HP components "binding" (the high pressure poppet, spring, balance chamber assembly) etc., and no restriction of airflow anywhere, then it is probably just the way that reg is.

Most of my 1st stages are balanced diaphragms, and many (most) balanced diaphragm 1sts are pretty similar in design.... my feeling is the only adjustment you can probably make to your 1st stage would be to adjust the IP pressure.

As far as "tuning": Typically, you set the IP of the first stage to "factory spec" (usually within a stated range of IP's), then "tuning" occurs at the second stage. With a diaphragm reg it is usually easier to vary the IP than with a piston, so in theory you can "tune" the first stage (by adjusting the IP within the specified range), but I think most folks consider the biggest effect on breathing effort to be how well the 2nd stage is adjusted (assuming the 1st stage is working correctly and within normal IP range).

Best wishes.