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So, I've got a perplexing problem with pressure gauge accuracy that's been bugging me for a while, and it's finally come to a head. I'm hoping someone can offer an explanation and possible solution. I've got a pressure fermentation currently in progress in a Unitank using WLP-808 "Mythical Hammer" mixed blend lager yeast that calls for warm temperature (63F) @ 1 BAR pressure. I'm monitoring the pressure with the tank's original equipment pressure gauge similar to this:
I'm controlling the pressure with a Spike Brewing combination spunding valve:
The Spike valve is a great innovation that combines pressure readings with spunding capabilities, a Gas In port for CO2 additional pressurization, and (most importantly) a built-in large disc PRV that dumps whenever tank pressure exceeds about 16-17 psig., all connected to a single 1.5" TC port. I've used the Spike valve several times as a stand-alone device to free-up a couple of TC ports on my unitank as well as simplify the installation and clutter of the various components during fermentation. I also have a Spike manifold:
...which was essentially replaced by the Spike spunding combination device.
Here's the problem. The gauges on both Spike devices appear to have significant errors. I first noticed this on the manifold device when I used it during forced carbonations. The beers seemed flat when I'd initially tap a keg, but later, after a few days in the kegerator, they seemed fine. The cause never got chased down since the problem 'solved' itself. Later after purchasing the Spike spunding valve, I started noticing that the PRV was releasing prematurely at around 10-12 psig instead of the designed release point of 16~17 psig. I guessed that the internal spring mechanism was weak, thus allowing the PRV disk to become unseated at a lower pressure. Not a big deal, since I would normally shoot for around 12 psi @ 48F when spunding, but it was an annoyance since, when cold crashing post fermentation, the carbonation level would drop below the desired 12 psi for volumes of CO2 at the cold crash temperature (38F). Once again, a few days in the kegerator fixed the deficiency.
So during this current fermentation, I mounted both the OEM pressure gauge and the Spike spunding valve on the unitank. The OEM gauge started showing a modest pressure increase not long after the 12 hour mark following the yeast pitch. There was a small volume of bubble activity in the spunding cup, but no indication of pressure rise in the Spike gauge. Eventually the Spike gauge began to show some increase by Day 2, but lagged far behind the OEM gauge. By Day 3 the OEM gauge registered 15 psig/~1 BAR, but the Spike gauge only showed 10.5 psig. But which gauge was indicating correctly?
Intuitively, it would appear that the Spike gauge was in error, since the difference of ~4.5 psig was about the same pressure that the over-pressure PRV was opening 'early'. But intuition doesn't constitute proof, so I attached two different Gas In post mounted inexpensive pressure gauges. Both they and the OEM gauge were all in agreement +/- 0.5 psi. It looks like the Spike gauge is in error by 4~5 psi, which is certainly not an insignificant value in this application. In retrospect the gauge on the Spike manifold is probably off by 3-4 psig as well. Maybe just a coincidence, possibly a random chance that I happened to get a couple of bum gauges from a very reputable vendor (Spike Brewing). who make some very high quality and innovative products.
One thought did occur to me. The OEM gauge and the two Spike gauges are both liquid filled (glycerin) damped gauges. The hand-held Gas In port gauges are cheap ($10) NPT mount dry gauges. There is no provision for periodic recalibration of either type of gauge. The liquid filled gauges however all come with fill ports with neoprene caps that are removable. Somewhere in my distant past memory bank I seem to recall that when they are filled and the cap is replaced, you 'seal in' the local barometric pressure. If that pressure is either abnormally high or low (deviating significantly from Standard 1013.4 millibars at sea level), then there will be an inherent error in any subsequent readings. If for instance the Spike gauges were manufactured and assembled in Denver (5230') on a low pressure day, they might indicate in error on a high pressure day in Death Valley (-200'). Don't know if that error could be 4.5 psig, hypothetically. But being cheap by nature, if I can pop the cap on these gauges to equalize the ambient pressure, I could save myself a few 'Benjamins' on replacement gauges.
Is this possible, or am I once again experiencing age-related misremembering induced hallucinations?
I'm controlling the pressure with a Spike Brewing combination spunding valve:
The Spike valve is a great innovation that combines pressure readings with spunding capabilities, a Gas In port for CO2 additional pressurization, and (most importantly) a built-in large disc PRV that dumps whenever tank pressure exceeds about 16-17 psig., all connected to a single 1.5" TC port. I've used the Spike valve several times as a stand-alone device to free-up a couple of TC ports on my unitank as well as simplify the installation and clutter of the various components during fermentation. I also have a Spike manifold:
...which was essentially replaced by the Spike spunding combination device.
Here's the problem. The gauges on both Spike devices appear to have significant errors. I first noticed this on the manifold device when I used it during forced carbonations. The beers seemed flat when I'd initially tap a keg, but later, after a few days in the kegerator, they seemed fine. The cause never got chased down since the problem 'solved' itself. Later after purchasing the Spike spunding valve, I started noticing that the PRV was releasing prematurely at around 10-12 psig instead of the designed release point of 16~17 psig. I guessed that the internal spring mechanism was weak, thus allowing the PRV disk to become unseated at a lower pressure. Not a big deal, since I would normally shoot for around 12 psi @ 48F when spunding, but it was an annoyance since, when cold crashing post fermentation, the carbonation level would drop below the desired 12 psi for volumes of CO2 at the cold crash temperature (38F). Once again, a few days in the kegerator fixed the deficiency.
So during this current fermentation, I mounted both the OEM pressure gauge and the Spike spunding valve on the unitank. The OEM gauge started showing a modest pressure increase not long after the 12 hour mark following the yeast pitch. There was a small volume of bubble activity in the spunding cup, but no indication of pressure rise in the Spike gauge. Eventually the Spike gauge began to show some increase by Day 2, but lagged far behind the OEM gauge. By Day 3 the OEM gauge registered 15 psig/~1 BAR, but the Spike gauge only showed 10.5 psig. But which gauge was indicating correctly?
Intuitively, it would appear that the Spike gauge was in error, since the difference of ~4.5 psig was about the same pressure that the over-pressure PRV was opening 'early'. But intuition doesn't constitute proof, so I attached two different Gas In post mounted inexpensive pressure gauges. Both they and the OEM gauge were all in agreement +/- 0.5 psi. It looks like the Spike gauge is in error by 4~5 psi, which is certainly not an insignificant value in this application. In retrospect the gauge on the Spike manifold is probably off by 3-4 psig as well. Maybe just a coincidence, possibly a random chance that I happened to get a couple of bum gauges from a very reputable vendor (Spike Brewing). who make some very high quality and innovative products.
One thought did occur to me. The OEM gauge and the two Spike gauges are both liquid filled (glycerin) damped gauges. The hand-held Gas In port gauges are cheap ($10) NPT mount dry gauges. There is no provision for periodic recalibration of either type of gauge. The liquid filled gauges however all come with fill ports with neoprene caps that are removable. Somewhere in my distant past memory bank I seem to recall that when they are filled and the cap is replaced, you 'seal in' the local barometric pressure. If that pressure is either abnormally high or low (deviating significantly from Standard 1013.4 millibars at sea level), then there will be an inherent error in any subsequent readings. If for instance the Spike gauges were manufactured and assembled in Denver (5230') on a low pressure day, they might indicate in error on a high pressure day in Death Valley (-200'). Don't know if that error could be 4.5 psig, hypothetically. But being cheap by nature, if I can pop the cap on these gauges to equalize the ambient pressure, I could save myself a few 'Benjamins' on replacement gauges.
Is this possible, or am I once again experiencing age-related misremembering induced hallucinations?