What is valve lock in a pneumatic gun?

by B.B. Pelletier

Two things drove me to this posting today. We had a reader from Hawaii whose AirForce Condor is not performing as it should, and another reader named baldtrucker asked what happens when a multi-pmp pneumatic like a Benjamin 397 is over-pumped. I did a search and couldn’t find where I had addressed this question before; but, even if I have, it’s time to do it again.

How does an impact pneumatic valve work?
The most common valve is the impact type or knock-open valve, and that’s the one that has a problem with over-pressurization. When a hammer strikes the end of the valve stem of an impact valve, it forces it to momentarily lift the valve face off the valve seat. When that happens, air can flow through or past the valve stem and out into the breech of the airgun.

The valve face is held against the valve seat by a return spring. Also, any air pressure inside the reservoir where the valve face and seat are located pushes against the back of the valve face, forcing it against the valve seal. These two forces (the return spring and air pressure) are what keep the valve closed.

The hammer has to strike the valve stem with enough force to unseat the valve momentarily, allowing air to flow from the reservoir. The weight of the hammer and the strength of the spring that pushes it have been calculated to open the valve when the pressure inside is at its maximum. For most multi-pump guns made today, the valve allows all the stored air to be released. That’s easy because their reservoirs are very small. But, precharged pneumatic reservoirs are larger and only a portion of air is released. The next time the valve opens, the pressure inside (pushing against the valve face) is slightly lower, so the valve remains open slightly longer. A little longer flow of air at lower pressure is released, giving the same velocity to the pellet. This is always easier to control when the barrel is longer, so long-barrelled rifles are generally the most consistent, though a valve can be tuned for any barrel length.

What happens when a pneumatic is over-pressurized?
When the air pressure inside the reservoir is higher than the design of the action can accommodate, the hammer cannot open the valve as far as it should, so less air escapes. That is exactly what is happening to the Condor out in Hawaii. The Condor valve face is HUGE! It has to be, to allow as much air as possible to move through the valve. However, such a large surface area means the valve is also EXTREMELY sensitive to air pressure. Any over-pressurization will hold the valve shut, so the pellet gets very little air to push it.

When you put air into an airgun, it is nothing like putting gasoline into the tank of a car. Even then, more gas doesn’t make the car go faster, does it? What a pneumatic gun needs is air FLOW, and that happens only when the valve remains open as long as it was designed to.

Condors do not like to be filled to 3,000 psi. I have seen only a few that would tolerate it. Most like to be filled to around 2,800 psi. And I have seen a few that liked to be filled to just 2,600 psi. No matter what pressure you fill them to, as long as it is their maximum pressure, they will all give you about 20-25 VERY powerful shots when the power setting it set on high. That may seem counter-intuitive to some, but consider this: A NASCAR race is not won by putting more fuel into the car. It’s won by making the most of the fuel that is put into the car.

The same thing happens when a multi-pump is over-pumped. I hear stories all the time about how so-and-so pumped up his Sheridan Blue Streak 20 times, and it cracked like a .22. I just smile and keep my thoughts to myself, and now you know why. A gun that is supposed to be pumped a maximum of eight times isn’t going to crack like a firearm with 20 pumps. It isn’t going to do much of anything; and if it does, that gun is already worn out and powerless.

Crosman had the answer!
In the 1950s, Crosman came out with a pneumatic valve that couldn’t be over-pressurized – at least not easily. They put it in the Crosman 140 rifle and the 130 pistol and touted it as the answer to over-pressurization and valve lock, as this problem is commonly known. The valve did work as advertised, however, it had a few drawbacks. As the pressure increased, the trigger became harder to pull. It was impossible to fix that, and the triggers were always second-rate. This type of valve had the habit of opening on its own when the pressure was still low. I’ve had guns fire while I was filling them – so this valve type was not the solution to valve lock that it promised to be. They also had the problem of the pliable parts of the valve extruding through the valve ports under pressure.

So, that’s the story on valve lock. It’s pretty straightforward. As long as you operate your pneumatics within the parameters that they were designed to operate, they will serve both well and long.

38 Responses to “What is valve lock in a pneumatic gun?”

  • Bob Says:

    So reading your post the solution for the Condor in Hawaii is to keep shooting the gun (or lower the pressure in the tank somehow else)until the pressure is below 2,800?

  • B.B. Pelletier Says:

    Bob,

    Forget the pressure. Just keep shooting until the power increases. WHATEVER that pressure turns out to be is the max fill pressure for that rifle.

    B.B.

  • Anonymous Says:

    so.
    overpumped Crosman1377 still has some unused air after shoot..

    and it is bad for the valve..

    5 extra pumps does not increace speed much..

  • Anonymous Says:

    B.B.

    Could we get a picture of the valve diagram so we can better understand what you are saying?

    Thanks.

  • B.B. Pelletier Says:

    Valve diagram,

    I’ll put it into the que.

    B.B.

  • Anonymous Says:

    Dear B.B.

    What about the PCP guns with a regulator? Do they have the same kind of problem that you described?

    Also, is the air regulator prone to break down due to the high air pressure (3000psi)?

    Jimmy

  • B.B. Pelletier Says:

    Jimmy,

    Homemade regulators do break down. In order to last, all the parts of the reg have to be either honed or burnished, but many home builders just turn the parts on a lathe and let it go at that. A professional reg will not break down for years.

    If you overpressurize a gun that has a reg, it will be the reg that is affected instead of the valve. The outcome is about the same, though valve lock doesn’t offur. But airflow through the reg will slow down and stop,

    B.B.

  • Will Says:

    Hi B.B.,

    I plan to get my first PCP in a couple months – a Talon SS.

    I want to chronograph shots to determine the combination of fill pressure and power wheel setting to get the lowest pellet speed variance and the highest shot count.

    Would you explain the concept of a family of “pellet speed vs power wheel” curves given a range of tank fill pressures.

    I think what I’m looking for with the chronograph is a Max pressure, Min pressure, and power wheel setting, right? Can you recommend how you would systematically test for this?

    As soon as you change barrel lengths, do you have to re-test? Would you please explain this?

    Thanks,
    Will

  • GadgetHead Says:

    Hi B.B. and all,

    I really enjoy your blog and I’ve learned alot from your articles and reader comments. Thanks one and all!

    Today’s blog is especially interesting because it’s on topic with research I’ve been doing for a couple of days now. It’s like some sort of a “Twilight Zone” moment!

    The other evening my neighbors and I were outside shooting the breeze, so to speak, about this and that. Talk turned to thinning the squirrel population. Sure, they’re cute but they are pests when they start chewing the wood moulding on your house.

    My neighbor still owns his very first air rifle… a Benjamin Model 3120 – 85 shot pump rifle

    [http://www.vintageairguns.co.uk/photo-library/photos2.asp?dir=%5BBenjamin+rifles%5D&pic=6]

    … and he got it out to show me. It’s still in good shape although the black has worn off in some places.

    It works well on the pest squirrels, too. He shot a pest the other day that got hung in the tree. A few hot Texas days later my neighbor was out working on a project and saw a vulture was in the same tree had found the carcass. Problem solved!

    So, anyway, he mentions that he pumps it up 11 strokes, but I noted a questioning note in the way he said that. Well, I thought that sounded a little excessive, but I’m not one to spout off about things I don’t know. It works for him so I decided to hold my tongue until I had correct information to share with him.

    My neighbor isn’t an ‘Airgunner’ [and I'm not sure I qualify for that handle either]. He just happens to still own his boyhood airgun, takes good care of it, and now uses it as a pest elimination tool.

    I knew some Benjamin owning boys a long time ago and I seem to recall their Benjamin pump guns had a maximum of 10 pumps. So far my Web research has only revealed to me that new Benjamin Sheridan pump guns allegedly deliver max. power at 8 pumps.

    What say you and your readers? What was the manufacturers recommended maximum number of pumps, for this vintage smooth bore, .22 caliber round ball shooting air rifle?

    Cheers,
    GadgetHead

  • B.B. Pelletier Says:

    Will,

    I suggest that you join the Talon Owners Group. There are even more things to consider – such as the height of the top hat.

    I won’t explain – you’ll find it all there.

    B.B.

  • B.B. Pelletier Says:

    GadgetHead,

    I will have to research the answer to this, because the 3120 is a strange bird – a repeating multi-pump. The earliest Benjamin repeater, the 600, was able to shoot several shots between pumping, and I think it was supposed to be pumped 20 times. I think the 720 was the last of the multi-shot on a single pumping and I believe the 3120 should be maxed at 10 pumps for just a single shot per fill. But as I said, I will have to research it.

    B.B.

  • Anonymous Says:

    BB,
    Could you explain the different types of pellets? Bearcub, Hollow point, wadcutter, and a few other types all see confusing. I plan on plinking, target practice, and shooting pests and I’m not sure which type is right for the job. I have an idea on brand and caliber, but the type is confusing.
    Thanks for the great blob.

  • B.B. Pelletier Says:

    Pellet types,

    Yes, I can do that. I’ll add it to the list.

    And thanks for the kind remarks about the blob!

    B.B.

  • mr-lama Says:

    The whole over pumping things sounds like what most everyone does when they are young and get their first mulit-pump. You think, if I pump it twice, it shoots slow, if I pump it ten times, it shoots faster. So to get it going as fast as possible you pump it thirty times. I’m sure most of us have done it, I know I have.

  • Anonymous Says:

    Predators may ingest the lead from a carcass. To be kind to predators, use leadless or get rid of the carcass.

  • GadgetHead Says:

    Hello Anon,

    You do have a good point there. Although vultures are infamous for their resistance to biologiccal toxins there is evidence that ingested lead can harm or kill a vulture.

    Unfortunately, I don’t know of any .22 round ball ammo that wouldn’t possibly damage the brass barrel of my neighbors air rifle.

    I guess this is a good example of how solving one problem can create another, and solving that problem can create yet another problem, and on and on…

    I’ll pass that along to my neighbor.

    Cheers,
    GH

  • GadgetHead Says:

    B.B. Pelletier said…

    I will have to research the answer to this…

    Thanks! I couldn’t ask for more and I certainly appreciate your efforts even if you don’t find a definitive answer.

    Call me a dreamer if you like, but I’m hoping someone who owns a model 3120 and still has the manufacturers literature will stumble across this blog and provide the answer.

    Cheers,
    GH

  • B.B. Pelletier Says:

    GadgetHead,

    Dean Fletcher published the owner’s manual for the 3120 in his book,”The St. Louis & Benjamin Air Rifle Cos.” and the maximum number of pumps for a 3120 is 12.

    B.B.

  • Mike in Iowa Says:

    A possible way to find the maximum pumps on a pnuematic multipump gun is to check after you have fired and see if there is any pressure left in the gun, just cock and fire if it goes poof then you have over pumped it…….?

  • B.B. Pelletier Says:

    Mike,

    That’s the way to do it. It’s also the way to determine when work needs to be done, if your gun accepts fewer strokes than it used to.

    B.B.

  • GadgetHead Says:

    Hello B.B. and Mike in Iowa,

    B.B. Pelletier said…
    Dean Fletcher published the owner’s manual…

    Ah! Dreams do come true! Thanks alot B.B. for taking the time to find the definitive answer for me and my neighbor. I saw Fletcher’s book for sale at several online retailers, but wasn’t inclined to spend $45 or so for the new book, or to start canvassing local used book dealers trying to find a used one.

    On the other hand, my neighbor may be interested in buying the book since you’ve now verified it contains the model 3120 owner’s manual for his air rifle.

    Mike in Iowa said…
    A possible way to find the maximum pumps on a pnuematic multipump gun is…

    Thanks for the tip/trick, Mike. I know next to nothing about the types of air valves used in pneumatic airguns, so I thought the valve on single shot multi-pump pneumatics just stayed open until the whole air charge was released.

    I’ll pass along your and B.B.’s follow-up tips to my neighbor.

    mr-lama said…
    The whole over pumping things sounds like what most everyone does when they are young…

    [LOL] Yes! My neighbor admitted falling prey to the ‘if this much is good, then more is better’ principle in his youth. Apparently that’s the only time he ever needed to have his Benjamin 3120 air rifle repaired since he got it, in 1977.

    Cheers,
    GH

  • Anonymous Says:

    bb.
    if i change the hammer spring with one that is twice as strong and/or replace the hammer with a heavier one, does that means that i can pump 16 times instead of eight into benjamin sheridan and have twice the power?

    and about the crossman airgun you mention, u say it cant be overpump, is it really so?
    i mean i have a sharp airgun and i never pump it more than 8 times. how to know the max pump in this kind of airgun?

    regars

    haque

  • B.B. Pelletier Says:

    haque,

    If you double the power of your hammer spring you run the risk of shearing off the bolt handle (on an older gun), and of breaking off the J-bolt on all guns. You would get a little more power (maybe 10 percent) but the pump linkage would wear out from the strain.

    The Crosman 140 can’t be pumped into valve lock, but the rubber seal can be extruded through the valve body. Your Sharp has the same kind of valve, so you can pump more times, unless you have a British model that has a release valve when the pressure gets too high.

    B.B.

  • Tony Rivera Says:

    So how can you increase the output of a multi-pump gun? Are there parts you can buy to increase the firepower? I just bought a Remington Airmaster 77, that I would love to modify and hot-rod out, if I may use your gas tank analogy…

  • B.B. Pelletier Says:

    Tony,

    The key to increased performance with multi-pumps and hot rods, alike, is increased gas flow. Anything you can do to get more pressurized gas behind a pellet will increased its velocity. Some of the tips to tuning are:

    1. A longer barrel,

    2. Increased dwell time on the valve,

    3. Enlarged air passeges in the valve,

    4. Smoothed surfaces in the air passeges to increase air flow,

    5. Cramming more air into the reservoir, and

    6. Increasing the caliber.

    B.B.

  • Anonymous Says:

    I have an archery barrel for a 10/22ruger.The barrel is made by swivel machine works and is most impressive in workmanship and accuracy. This company use to make a pnuematic version that shot a 16” airrow over 600fps. they stoped production because they were to expensive for most people to afford. I am considering purchasing a condor or a talon in hopes of having my archery barrel tooled to fit the action of one of these airforce guns.Im not looking for 600fps, 1/2 that would be fine.
    Being that the airforce guns are not cheap can any one tell me if what I propose is Doable? and any problems I might encounter.

  • B.B. Pelletier Says:

    I tested the Archery version of Swivel Machine Corps gun and the best I every got was about 430 f.p.s. from a lightweight aluminum bolt.

    There is a man in Virginia who does the conversion you are wanting.

    http://www.axiomlemak.com/index.htm

    B.B.

  • Mark Says:

    Hello!
    I purchased two air rifles from a local gun shop back in Syracuse, NY in the Winter of 1985. The first was a Benjamin model 3100…BB, the second is my 3120…22 cal round lead ball 85 shot. My 3120 is still in the original yellow,blue and white box and is in like new condition. I still have NOT opened the yellow envelope with sample ammo yet. Anyway, I read your comments about overpumping and since I have two mint copies of the instruction sheets (not a manual) It states: “INSTRUCTION SHEET FOR NO. 3100-3120 BENJAMIN SUPER REPEATER AIR RIFLES KEEP FOR FUTURE REFERENCE…..below near a sketch of a air rifle being pumped is the following paragraph: SHOOTING FORCE IS ADJUSTABLE. You can determine number of pumps required for various uses after a little practice. Pump four or five times for ordinary shooting; for harder shooting pump 10 or 12 times.

    Best Wishes,
    Mark

  • B.B. Pelletier Says:

    Mark,

    Thanks for your message. Both guns are repeaters, but both shoot just one shot per fill, I believe. Therefore, the number 12 is the highest number of pump strokes I have heard of for one shot from a multi-pump.

    B.B.

  • pellhead Says:

    On the Benjamin long guns. 50′s vintage guns like the 310,317, and 322 said “10-12″ pumps max while modern counterparts say 8 max. The old designs had a cavity in the pump cup so that the whole stroke volume didn’t enter the inlet, which gave some rebound on the next pump. Modern cups stuff most of the stroke. I took off some (the old guns)on the outlet valve spring to allow full release of the chamber. Too much of that and the outlet might not close even with the hammer back. Modern design has full release. Overpumping is going to crush the seals on the valves. I wish I had the old simple, smooth, light trigger back.

  • Anonymous Says:

    I might have over pumped my air rifle by not counting how many pumps I’ve made because I wasn’t paying attention a few times, I probably pumped made about 5 extra pumps or so, but so far my gun shoots fine, I think… My question is that how can you tell if you have done damage to the air rifle by over-pumping, does “damage” come in the form of wear and tear and “hidden” or “latent” damages that you don’t find out until over the years you realize that the velocity isn’t as good as it used to be or having leaks here and there, OR does the damage caused by over-pumping is sudden, very noticeable change in the gun’s performance, like when you over pumped it and it caused damage, you right away notice something apparantly different about your gun that you can’t miss.

  • B.B. Pelletier Says:

    Damage,

    You can damage a Sheridan pump in two ways. First, you will cause the general wear to be accellerated and the gun will need to be resealed sooner. Second, there is a shear pin inside the gun that will fail if exposed to too much effort. When that happens, the gun stops workijg immediately.

    Both situations are repairable.

    B.B.

  • Dizan Says:

    Hmm well I dont believe this to be true…
    I have a Daisy Powerline 880 (Cheapo)
    I tested it with pellets just to see if this theory was correct, well on this gun it is incorrect.
    10 pumps (maximum) is good enough to deep dent a 1/8″ sheet of hard plastic
    30 pumps is enough to blow through 2 sheets of 1/8″ hard plastic, 1/4″ wood paneling, sheetrock, and lodge into a 2×4 stud.
    So something is off. As for sounding like a .22 not at all 10 pumps, but at 30 pumps its pretty loud.
    As for going over 30, I’ve done 45 pumps and havnt noticed any difference in power…it just gets louder, so I remain at 30 for the once in a while long range..but I think the main reason it keeps working is that I’m useing heavy duty axle grease to lube all the parts (cept the air flange)
    Tell me what ya think of this little bit!

  • Anonymous Says:

    In response to Dizan, to an extent and depending on the rifle it isn't true. Each rifle is different and there tolerances are different. Air rifle experts cater to air rifle manufactures. It's what keeps them blogging. If they told someone they could over pump their cheapo pneumatic and take out small game at 50 Yds. how many $400 air rifles would be sold?

  • Vince Says:

    Anonymous, one doesn't need to spend $400 on an air rifle to take game out to 50 yards. A sub-$200 TF89 or MP513 will do it nicely. Some have been able to do it with a sub-$150 Gamo Big Cat or a sub-$100 Crosman Quest. Yet the $400 guns still sell.

    Even if a particular Daisy 880 WOULD give a normal service life constantly being overpumped at 30 strokes, that's a real pain in the keester. Pump a gun 30 times as opposed to once for a good springer? Most people value their time more than that…

  • turner Says:

    this is just like how people sweet spot auto cocker paintball guns. look into that if you want more examples.

  • Anonymous Says:

    so if this is true then how do people get way better FPS just by adding a flat-top piston and valve? doesnt that significantly increase the amount of air thats pushed into the valve?

    im making this statement based on the 1377 i just got and did a few mods on. im thinking of getting a benji 392 and was hoping i could do the same mods to it. is the valve different or something? do you know of any mods i could do to a 392 if i got one? i really enjoyed customizing my 1377

    where can i see a diagram of the gun/valve?

    -trevor

  • Bruce Says:

    trevor,

    It's nice to see a new person posting–welcome. You asked your questions on a blog that was written in 2006. There is just a samall handful of us checking the older blogs.

    I don't have the answer to your question, but if you repost it on the current blog, off topic questions always welcome, someone will have the answer for you. http://airgun-academy.pyramydair.com/blog

    Hope to see yoy there trevor!

    Bruce

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