Air Venturi hand pump: Part 2
by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- The great challenge
- An experiment reveals a lot
- The trick
- The dawn of modern high-pressure hand pumps
- The Air Venturi G6 pump
- Today’s test
- My physiology
- The test plug
The great challenge
Writing about the Air Venturi G6 hand pump is one of the most difficult reports I’ve ever attempted, because most airgunners know so little about hand pumps in general, and a lot of it is wrong. Also, because the audience for this subject spans the gamut from rank beginners to people who have owned other hand pumps for years, the spectrum of comprehension is infinite. Some people feel this is nothing more than an expensive bicycle pump, so I have to explain how it is different.
I read online discussions of hand pumps among airgunners, and I can tell that only a few of them have any actual experience. It goes beyond the blind leading the blind — it’s more like the blind writing detailed travel instructions to places they’ve never been.
The only way I can think of writing this report is to write it as though my readers have no idea of what high-pressure hand pumps do. Here goes.
Pneumatic airguns have been filled by hand pumps for many centuries. They were specifically made for the guns they serviced — there was no interchangeability or interoperability in those days. So each pump you encounter will be unique. Only in the late 19th century do we start to see similar hand pumps coming from makers. That was probably because the tooling they used to make their pumps dictated what they were able to make — so they repeated their pump designs and specifications for their own convenience.
An experiment reveals a lot
Until Dennis Quackenbush and I experimented with handmade hand pumps that mimicked the pumps of antiquity, I never saw anything in print that reported their performance. Writers mentioned that they were used and how they operated, but nobody said anything about what they could do. Dennis wanted to see what these old pumps could really do (he knew, but he wanted to let me write about it), so he sent me some pumps that were rigged up as test fixtures for me to test. I first wrote about them in Airgun Revue 4 and then repeated that article in a special three-part blog series.
If you are curious about how hand pumps operate, I highly recommend reading that report. To my knowledge, nothing like it has ever been written, before or since.
What we learned was that airguns could be filled to pressures as high as 800 psi with these simple pumps, but it took a very heavy person (240 lbs.) to go that high. That weight is far beyond the average for men of the 17th and 18th centuries. Weighing around 130-150 lbs., they weren’t going to be able to fill as high — it is a physical impossibility. So, the guns they filled had to operate with pressures below 800 psi. Perhaps 500-650 psi might be a more realistic number.
To pressurize air higher than these antique pumps went takes a smaller pump piston, so the weight or force that’s available can be less. But a smaller pump head means less air (by volume) is compressed with each pump stroke. It is possible to build a hand pump that goes as high as 2000 psi, but because of the very small pump head the number of pump strokes that are required to fill a reservoir with air to that level jumps from a couple hundred to several thousand. It just isn’t practical.
What was needed was a breakthrough in pump technology. A hand pump not only had to have an ultra-small pump piston head, it also needed a larger pump piston head, so the filling would go faster. The solution was a multi-stage pump that contained both sizes of pump heads, working together.
The dawn of modern high-pressure hand pumps
The airgun world was shocked in 1995 when the world’s first high-pressure hand pump hit the market. It was made in Europe and allowed a person to fill a pneumatic airgun up to 3,000 psi. It worked, but there were some serious caveats to how well it worked, because the same physics of the old days were still working. There were not two but three different size pump heads inside the new pump — one nested inside the other. As the pump handle was operated, each pump head fed air into the next stage, where it was compressed higher until the output was an extremely high 3000 psi with the pump force remaining relatively low. This was the modern three-stage hand pump.
However, the term “relatively low” has significant meaning. The force required to pump the new pump was a small fraction of what it would have been if it was a single-stage pump, but it still wasn’t that small. It hovered around 160-180 lbs. that were needed to force the pump handle all the way down. The men of the 1700s would have hailed the modern three-stage hand pump as a miracle, but the men of the late 20th century thought it took a lot of work to fill an airgun. And they were right. Lighter people and people with weak wrists found they could not pump past a certain pressure level. That was why the Benjamin Discovery that only fills to 2000 psi was such a breakthough air rifle.
Okay, that was the genesis of the modern three-stage hand pump. Over the 20 years they have existed, I have read several claims about marvelous technological advancements. I have tested most of these claims and found them to be false. Physics is physics, like the man said. There is a potential advancement that inventor Bob Moss created that I have called the “butterfly” hand pump. It uses a moving pivot point on both sides of the pump rod to magnify the effort applied to the downward stroke of the pump handle, but to date this advancement has not been produced.
The butterfly hand pump would significantly reduce the effort required to reach the maximum output pressure.
The Air Venturi G6 pump
Having said that, I will now tell you that there isn’t much difference between any of the hand pumps on the market today. Some have desiccant filters that dry the air as it’s drawn into the pump, and all have some kind of moisture trap on the output end. That trap is often packed with small glass balls that allow moisture in the hot compressed air to condense on their relatively cool surfaces. When you bleed the air line, the pressure inside the chamber at the base of the pump rushes out rapidly, carrying all the condensed moisture with it.
I find the Air Venturi G6 pump to be far smoother to operate than the first pumps of the 1990s. The outer pump shaft is finished much finer. Even my 10-year-old Hill pump is rougher than this new G6. What that means is the main pump shaft slides up and down with less friction, and that means an easier pump stroke.
Today I will pump the pump against its test plug and tell you what I find. I did that it Part 1, but today I’m more aware of the pump because I have handled it more.
To understand what I’m about to report you need to know something about me. I al 67 years old and in generally good health. I exercise 7 days a week. My resting heart rate is 52 beats per minute when I awaken and 61 bpm at any time during the day. My blood pressure at rest is about 125/72 these days. I am 5 feet 10 inches tall and weigh 220 lbs. I am relatively active for my age and can outwalk most people of any age. This is the person who is about to pump the G6 for you.
The test plug
The G6 comes with a brass plug that can be inserted in the female quick disconnect coupling at the end of the hose any time you want to test the pump. Since it blocks the airflow, you have a contained circuit to test. This allows you to test the number of pump strokes it takes to fill the pump hose to a certain pressure.
I found the test plug difficult to insert in the coupling on the hose until I chamfered the edges that push the ball bearings back inside the quick disconnect. When I did that, the plug went in, though it fit very snugly.
In Part One I linked to a video I made on using a hand pump in 2006. If you are new to hand pumps you really need to watch it, because it shows the right way to pump an airgun. Near the end when the pressure has increased you use the entire weight of your body to press down on the pump shaft. It is vitally important that the shaft goes all the way down, because stopping one inch before that point wastes 50 percent of the air that was compressed by that stroke.
Using this technique, I pumped 5 strokes to fill the pump hose to 100 bar/1,450 psi. That was easy! Then I continued to pump until I had put in another 10 strokes — making 15 strokes in all. I wasn’t watching the gauge, but on stroke 16 I reached the point that I could no longer pump the pump.
Imagine my surprise when I saw that 15 pump strokes had increased the pressure in the hose to 300 bar/4,351 psi. I did that! Me — a 67 year old fat man! That’s why I told you about my physiology. Watch the video, then compare yourself to me and you’ll get a good idea of whether you can use a hand pump to fill a PCP. Reread Part 1 to see my recommendations about which airguns to fill and which ones to leave alone.
I tested it again to see the point at which the pump strokes became difficult for me. That happened on pump stroke 9, when the oil-filled gauge read 170 bar/2466 psi. That’s about the same as all other hand pumps I have used over the years. If anything, the G6 pumped a couple hundred psi higher before becoming difficult. I also noticed this pump is very quiet as it works. My Hill pump is very noisy and so have all other pumps I have used over the years. This one seems much smoother and quieter.
Will it last?
Back in the early days, hand pumps were difficult to maintain. They failed for one of two principal reasons. Either the owners had removed the moly grease from the pump shaft — thinking it was dirt — or the smallest o-ring at the end of the smallest pump head failed from overheating.
In the 20 years pumps have been around, manufacturers have learned how to make them better. The smoothness of the main shaft on this G6 pump is evidence of that. And I bet they have found a small high-temperature o-ring for the critical spot inside.
Besides that, hand pumps have become easier to repair. The G6 comes with 5 sets of replacement o-rings, so they want owners to have them when things fail. Back in the early days, replacement parts were extremely hard to come by.
I have said many times in this blog that hand pumps do not typically fail unless their owners do something wrong. Pumping too long (over five minutes per session) or too fast is one thing that can destroy a pump. Failing to go all the way to the bottom of the pump stroke is another thing you have to watch for, because if you do that you’ll have to pump many more strokes to fill your airgun.
Some owners remove the grease on the outer pump shaft, then they notice that their pump handle failes to stay down after a stroke. The lack of grease allows the outer o-ring to roll out of its groove — setting the pump up for this condition.
There is no way I can tell you how long a G6 pump will last before it needs attention. All I can do is point to the many hand pumps I have owned and tell you that most of them lasted over a decade. But I no longer fill my airguns with a hand pump. I have a compressor that I use to fill by carbon fiber tank, then the tank fills all my airguns. That’s the easier way to fill guns, but the tank and the compressor I own cost a total of $2500. If I were just starting out a hand pump would look more attractive.
You have to make the decision whether a hand pump is right for you. I tried to explain in Part 1 how to do that. If you do decide to get one, I think the Air Venturi G6 pump is a good one.