Why put a gauge on the plenum?

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JimD

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Mar 27, 2021
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I have 6 PCPs. One unregulated. One regulated with a gauge on the plenum and on the air storage cylinder. Four with a gauge on only the air storage cylinder. I admit I like having the gauge on the plenum because it lets me know where the regulator is set making tuning a bit easier or at least more certain. But if I shoot the 4 without a gauge down to where the guns come off the regulator and look at the tank gauge I know where the regulator is set too. Just takes longer.

The disadvantages of the additional gauge are several. It costs a little more and getting it on the gun takes some additional engineering and may take more parts than just the gauge. Neither the plenum or the bulk storage gauge on my guns seem to be terribly accurate. If you shoot down to the level of the plenum gauge on the bulk storage gauge and your velocity is consistent you are left with indecision. Which gauge is at fault? What does it mean about filling the gun and setting the regulator?

But another more subtle issue it can create is the users may complain about regulator creep. Every time I see this complaint I wonder if the user is complaining because their velocity is changing or because the gauge doesn't seem to read the same as it did when they last looked at it. I'm thinking it more probably the latter. If the velocity is not changing how much difference does it make if the regulator did move a little? How do you know it isn't just the gauge? Remember they are not expensive ultra precise measurement tools.

I'm ambivalent about having two gauges. I see advantages of the extra gauge but I also like relatively small light guns. If it seems like the additional gauge is not there because they were trying to make the gun smaller or lighter or less complicated I am OK with it.

Opinions?
 
It becomes a nice touch if your doing power / set up changes, as it speeds up the tuning process a lot !!
Also nice to monitor If Or Not the regulator set point is creeping, while also telling you when your just at the set point or past as that's the only time the gauge drops in shown pressure.
 
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For an expert like you, Scott, I accept the gauge is a plus. I am just not sure that it's completely helpful for those that are totally reliant on what the gauge says and don't bother to see if their velocity changed. If the gauge seems to have changed but not the velocity I think it becomes unclear. Either the plenum pressure didn't really change (just the gauge) or the pressure change was not big enough to affect the velocity. Either way the gauge pressure is only an indirect measure of what we really care about (velocity).

Another way to say what I thinking would be that more data is beneficial if you know what to do with it. To me, unless you know the gauge is dependable the first thing you do if it moved is to check velocity. Gauge movement could be a regulator problem but it also could be a gauge problem. With no gauge to stare at I just have to check velocity. Another potential complicating factor is temperature. You know velocity changes with temperature and how much. I am learning. But a velocity change from temperature in the direction of an apparent plenum pressure change could get a little difficult to interpret.
 
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JimD said:
...But another more subtle issue it can create is the users may complain about regulator creep. Every time I see this complaint I wonder if the user is complaining because their velocity is changing or because the gauge doesn't seem to read the same as it did when they last looked at it. I'm thinking it more probably the latter. If the velocity is not changing how much difference does it make if the regulator did move a little? How do you know it isn't just the gauge? Remember they are not expensive ultra precise measurement tools....
Click to expand...

But if the gun doesn't have a regulator gauge then the user will need a chrony in order to measure if the velocity is changing due to reg creep, which is fairly common. So in that case we have just swapped one measuring instrument for another. I think chronys are vital tools and I use mine often, but the reality is that the vast majority of airgunners do not have one. So the reg gauge provides very pertinent info to them at a glance.
 
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It gives the gun another potential leak spot too. For a hunting gun I want as few parts, and holes in any place under pressure, period. Dependability is key in the middle of nowhere. For fast paced competition guns though, all guages and knobs that help you get back up to speed or monitor the status of things are a definite plus. You can add hunting guns that you change projectiles, weights, and power, on the fly for, to this list too. Though I don't think many people besides those few on these forums actually ever do that in practice.
 
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I only have one regulated rifle and I am glad it has a gauge on the regulated side. It's a good indicator that everything where you left it. I check that gauge and the reservoir pressure gauge (among other things) as a pre-flight check before shooting. Not 100% necessary, but it is reassuring to know there's pressure there. My particular gun would not take kindly to a strike on the valve stem with no pressure. Likewise, I would also know if the reg was creeping up since that would indicate a problem I'd like to fix. I am a bit on the nerdy side, so I'll take all the info I can get about the health of my gun.
 
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I like light comparatively simple rifles like my P35s. I can change the regulator in them in 15 minutes or less even though it is inside. degassing and refilling take the most time. Most guns have to be degassed to go down in reg pressure so it doesn't reduce the speed of making a change that much IMHO. I also like to just get them where I want them and leave them alone (at least for awhile). I do like the little paper tape Huma puts on their regulators so you have some idea of the setting. I'm not trying to say I don't want a gun with a gauge, just that it isn't a big deal to me either way. If it saves the manufacturer money and that is reflected in the guns price and the other features are good, a gun without a gauge on the plenum is fine for me.
 
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One of the reasons I question the value of a gauge on the plenum is the sort of gauge that is used. You can buy one on Alibaba for under $4. A gun manufacturer probably pays closer to $1 for that gauge. How dependable do you think that $1 gauge is? It is not more dependable than a $30 chronograph. I kind of like having one too but there is no way I would trust that gauge over a chronograph. If I was a manufacturer knowing full well the kind of gauge I would be using I would be a bit reluctant to spend the engineering to get it on a gun knowing that customers would start calling me complaining of regulator creep based entirely on what that little $1 gauge says. Never bothering to check the velocity to see if the regulator has really moved enough to be detectable.
 
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JimD said:
One of the reasons I question the value of a gauge on the plenum is the sort of gauge that is used. You can buy one on Alibaba for under $4. A gun manufacturer probably pays closer to $1 for that gauge. How dependable do you think that $1 gauge is? It is not more dependable than a $30 chronograph. I kind of like having one too but there is no way I would trust that gauge over a chronograph. If I was a manufacturer knowing full well the kind of gauge I would be using I would be a bit reluctant to spend the engineering to get it on a gun knowing that customers would start calling me complaining of regulator creep based entirely on what that little $1 gauge says. Never bothering to check the velocity to see if the regulator has really moved enough to be detectable.
Click to expand...

If I am heading out on a hunt before daylight in the morning, I do not want to chronograph the gun. I want to look at a gauge and know that it is normal.
 
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JimD said:
One of the reasons I question the value of a gauge on the plenum is the sort of gauge that is used. You can buy one on Alibaba for under $4. A gun manufacturer probably pays closer to $1 for that gauge. How dependable do you think that $1 gauge is? It is not more dependable than a $30 chronograph. I kind of like having one too but there is no way I would trust that gauge over a chronograph. If I was a manufacturer knowing full well the kind of gauge I would be using I would be a bit reluctant to spend the engineering to get it on a gun knowing that customers would start calling me complaining of regulator creep based entirely on what that little $1 gauge says. Never bothering to check the velocity to see if the regulator has really moved enough to be detectable.
Click to expand...

My $1 gauge and $25 gauge both read the same.

-Matt
 
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From an tuning perspective, the reg does not need to read the exact presise pressure. If it read 10 bar to much or to low is not that important. The most important is that it does not fluctuate, fooling the owner thinking the reg is faulthy. And that it is possible to read the difference in at least 5 bar steps, on the scale. Most which adjust the reg, will do it together with a chronograph, which is a more important tool.
 
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I have regulated guns that fall into three main types, with respect to the use of gauges:
- Two gauges, covering both the regulated pressure and reservoir pressure
- One gauge on just the reservoir pressure
- One gauge on just the regulated pressure

Of the three, I like the two gauge set up best - especially since those are both high shot count guns. I do look at both gauges, one to see how much air is left and the other to see if the reg is still stable, especially if it has set for long time - occasionally I have felt the need to blow off a shot a too before taking a shot I care about if I feel the reg has creeped up more than normal.

After that, if I can have only one gauge, I prefer it on the regulated pressure. I know how much I fill the gun with the fill devices gauge, so being able to see that gun is "ready to use" with enough air for at least a few shots is best, and I know that the reg is still stable. One the one gun with only a fill pressure gauge, I have no idea if the gun is still working properly without shooting a string over the chrony. That is my least desirable set up.

I will say that most of my regulators are Huma regulators, and since I have several I bought Huma's regulator tester. I find that it is a great tool to have, and I have great confidence in knowing what the regulator is set to before it goes back in a gun. That also lets me know how far off the regulated pressure gauge is, and I don't worry about it - I just read it to see if has changed.
 
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