This PCP Airgun Fill Connector Incompatibilities post is the second in a three-part series. It is an up-dated version of an investigation that was originally published in Hard Air Magazine back in 2022.
So why are we looking at this topic again? There’s two reasons.
Firstly, as ever more PCP air rifles are sold, more enthusiastic, new airgun shooters will encounter issues related to PCP airgun fill connector incompatibilities. The problems have not gone away, they are being discovered every day by newcomers to our interest. This series is intended to help them – maybe you!
Secondly, it’s just in the nature of Internet publishing that historic posts become less easy to find – even if they are about important issues that are still relevant. So, it’s time to raise this topic back into improved visibility. Here we go again…
PCP Airgun Fill Connector Incompatibilities – Background
In order to understand PCP airgun fill connectors – particularly why some fittings don’t fit – the HAM Team measured no less than 108 male and 73 female quick disconnects. By analyzing this hard data, we were able to draw some basic conclusions.
1. There are no standard, published specifications for PCP airgun fittings.
2. PCP fittings are often described as “paintball standard”, “1/8-Inch NPT Quick Disconnects”, or “Foster fittings”. But none of these terms has a precise, specified, or documented definition. They are all just generic terms.
3. With ANY manufactured product, there WILL be variations between individual samples of “the same” part. These manufacturing tolerances mean that the actual size of any part may vary from the design specification – sometimes significantly.
4. For this analysis, HAM has measured JUST ONE DIMENSION for each of the male and female quick disconnects. This is – we believe – the most critical dimension that governs if males and females will fit together.
However a full engineering analysis of all the dimensions for both connectors should be made to completely understand the issue. This is beyond the HAM Team’s capabilities. It’s an issue for the whole airgun industry…
PCP Airgun Fill Connector Incompatibilities – Measurements
To understand the issue, we measured the Outside Diameter (O/D) of the male fittings.
In addition, we measured the corresponding Inside Diameter (I/D) of the balls inside the female fitting – with the collar out. That’s the largest I/D the female can accommodate.
Then we plotted all the measurements onto this chart. The female measurements are in red, males are in green. Both O/Ds and I/Ds are measured in Thousandths of an Inch, the left
axis of the chart.
Let’s now take a close-up look at the left side of the chart. Here we can see that the largest male measurements (mainly 309 Thou) are just 1 Thou less than that of the smallest female I/Ds. That’s close to being a very tight fit!
Statistically, it’s likely that – if we had a larger sample size – we would find some males that have the same O/D as the smallest female I/D. These would not fit.
Indeed one male O/D was 313 Thou. It’s the red line on the far left. That’s much larger than the smallest female I/D.
In fact, as you look across the chart, you can see that it’s larger than the majority of the female I/Ds. So, it will not fit any female with an I/D of less than 314 Thou. And – relatively speaking – there’s not many of them with a large enough I/D.
So now we can see why some HPA fittings don’t fit.
PCP Airgun Fill Connector Incompatibilities – “Known Good” Measurements
First let’s look at some Crosman male fittings. We know that Crosman has this issue under good control.
Now we can look at the Foster females. Note that we measured 16 genuine Foster parts. The additional 57 females we measured came from other manufacturers. That explains the spread of female I/Ds beyond the range of 311 – 315 Thou we measured for the Foster parts.
The design spec for the Foster female I/D looks to be 312 or 313 Thou.
Allowing for manufacturing variability between the largest Crosman O/D (309 Thou) and the smallest Foster I/D (311 Thou), that difference is just 2 Thousandths of an Inch. That’s small, although OK for our purposes.
And with a larger sample size, we’ll inevitably see greater manufacturing variability. Now there’s going to be situations where HPA fittings don’t fit.
What If Your PCP Fill Connectors Don’t Fit?
Sadly, the only answer is to try a different combination of fittings :-(
Based on this HAM analysis, we’d suggest you measure the O/D of the male fitting using a digital caliper. Then you can compare that measurement against the numbers in this HAM story.
Now at least you’ll have an idea of how likely you are to find a corresponding female that will fit the male you have.
As we’ve said before, the real answer lies in the hands of the industry. However, as ever more people start to use PCP airguns, these PCP fill connector incompatibilities are likely to become an ever-larger issue.
The post PCP Airgun Fill Connector Incompatibilities appeared first on Hard Air Magazine.
