Big bore pumper project...

[Duane38]

Hello!  Hope everyone has been doing well during these strange times!  I'm back again.  Life has had me very busy.  Certainly the same for many here, I'm certain.

Just received all the necessary metal to begin my next build.  This idea I have kicked around going back to the Crosman Green Forum.  A while.

So, this build will be a 9mm MSP build.  Will be using 1" bore pump tube and one of two valve designs.  Stuck between the typical poppet knock open and a dump valve similar to that used in the SSP. 

Nothing too magical here.  Pretty much a scaled up version of any other MSP.    Though, a nice long lever handle for reduced effort.

Don't be nay sayers either!  The .22 SSP builds enormous pressure with its 1.375" piston and first, assuming glance 9:1 lever ratio.  More on levers.....

Turns out that the systems in MSP air guns are not generically a Class I, II or III lever doing the work.  More of a compound working of levers comprising of two lever systems working together is how I look at them, further creating greater mechanical advantage; the progression of angular deflection of the link in relation to handle. 

Dunno really, but test, after test a few years ago on a rig mockup proved my hypothesis to rather accurate.  Led me to study full sweep of lever degrees in relation to toggle link degrees then the distance piston moves along the arc of the lever.

If the pump lever was truly, for example 9:1 ratio in its seeming design from the standpoint of lever points, the piston would move at a fixed distance per degree of movement with the lever.  Guess what, of course?  They do not!  I digress.

At any rate, let the build begin!

[RBQChicken]

Following!

[JuryRigger]

Welcome back to the forum; only a new(ish) guy here myself. Sounds interesting; am working on a ACP pumper and am interested in your designs/knowledge. Just so you know; this should be in the "Machine Shop Talk and Airgun Parts Machining" gate; you currently have this posted in Shadow's Place.
Will let a mod know to move the thread; no biggie. 
Take care,
Jesse

[Duane38]

Oops!  Wasn't sure if the right place, or not.  So many options...  Didn't see any related multi stroke pneumatic forums.

[JuryRigger]

Since you're building a whole gun and not just modding; the Machine Shop gate is the best place. Will get you more responses, too.
Good luck on the build, sounds very cool.
Jesse

[JPSAXNC]

Hi Phil, Have you decided what the valve volume will be yet?  James

[Duane38]

Hi Phil, Have you decided what the valve volume will be yet?  James

This Mr. Perotti?  Excuse me if I botched your name!

Yes sir.  Going with a 20" barrel, so the valve volume will be around 13cc.  May go a little bigger, then use a sleeve to reduce it if necessary.  Plan on equipping the valve with an air gauge for visual observation and research purposes. 

[JPSAXNC]

Hi Phil, Yes, it's me. I'll be following your build, it sounds very challenging. There was a guy named Zack on the old green forum that built a 9mm pumper, but I missed his build threads.

[Killercrow]

I'll be interested in seeing where this goes. I have always wanted to build my own pumper. Might as well go big!

[Duane38]

Made some chips fly last night.  Got the breech pretty much worked out.  A few little things to do such as the transfer port and bolt lug slot.  The bolt on this will protrude out the rear rather than the side like the Crosman sorts.

The underside has a rather robust saddle area to rest on the tube.  Saddles about 25 percent of the radius. 

On this build, I may try my hand at home anodizing in various color schemes.  Need to do some research and learn how. 

[Rob M]

Nice work Phil , love all the radii. following along

[rsterne]

Very nice job....

Bob

[Duane38]

Thanks, gang.  Through this week and weekend hope to get rear plug and valve completed. 

Purchased an Mrod stock from a member.  As you can guess, stock and trigger housing will be the Mrod. 

Pretty straight forward build, really. 

[JuryRigger]

Looks good;
Jesse

[sb327]

Excellent work there! Following along as well. I do enjoy a build like this.

Dave

[rsterne]

Here is a force diagram at 1500 psi for a stock Benjamin 392 pump (0.775" tube ID), showing how the pump handle force falls off in the last 10 degrees of pump stroke (red line)....



The blue line is for a sliding link arrangement, where the link starts 5.5" from the pivot and slides down to 2.5" as the pump lever passes an angle of ~60 deg. to the pump tube.... This was the optimum ratio I determined for the Benji pump.... The link slides automatically as the angle of the link to the pump lever passes 90 deg.... IIRC, the stock link is 4" from the pump lever pivot....

Unfortunately I no longer have a link to a photo showing how the linkage works, but the idea (not mine) is simple enough.... The link rides in a slot in the pump handle.... You can alter where it "shifts gears" by changing the length and location of the slot (and the length of the link arm).... The closer the near end of the slot is to the pivot, the longer the link arm gets....

Bob

[Duane38]

Hey, Bob.  Always enjoy your constructive  input on these creations.

On the SSP .22 I built, it utilizes a clone of the Benji lever regarding link length and pivot hole spacing.  That particular gun has a 1-3/8" bore pump tube and pushes wee bit over 11ci of air into a valve plenum size of .08ci. 

Right at the point where the utmost resistance is felt upon closing the lever home, it is immediately gone upon closing.  Credit, the lever is 22" from front pivot hole to lever end.  The hardest point is 54 pounds of force max.

With that being said, the theoretical piston load should be 3k pounds.  Using formulas for levers that don't take sliding sled into account (totally changing what they actually do) I shouldn't be able ro close the lever very easily!  Welp, the math works out more to be 55:1 instead of 5:1 based on the lever characteristics alone.  If it were 5:1, I'd be sharing a different experience with that gun.

This big bore using a 1" bore tube shouldn't present any woes, I don't think.

Some years back I posted these findings and a graph on the Yellow using the degrees of travel and loads with air gun MSP levers using my own build...  Surprisingly, the math worked out pretty darn close.  Within a few percent deviation. 

What I learned: MSP levers do not fit into any one of the three primary classes of levers.  Mainly due to the deflection and travel of the load. 

For sure, however, any sort of clever lever design certainly removes unwanted effort. 

What you reference reminds me of an SSP designed by Bowkett (sp?) Years ago.

*EDIT*

Will dig out my notes...  IIRC worked out to be the ME sum of the piston travel to lever travel of its circumference arc multiplied by the ME of what the lever alone is.  Something along those lines.  The two work in unison to accomplish a single goal in MSPs. 

I know.  Sounds completely whacky.

[Insanity]

Tuning in for this build.

[rsterne]

You can calculate the ACTUAL mechanical advantage by dividing the distance from where you apply the force to the pump lever by the distance the piston moves.... It is different for every degree of travel of the pump lever.... The MA actually becomes infinite (in theory), just at the lever closes, because the piston stops moving towards the valve just before the pump handle hits the bottom of the pump tube (because it rocks over center a fraction).... However, when the pump lever is at about 10 deg., it is only about 10:1 for many MSPs....

Bob

[Duane38]

It all appears to be that at first glance.  Aren't these compound levers?  Each MA (don't know why my auto correct wants to put 'ME') is multiplied to find the overall MA.

For example. The large tube SSP.  It isn't 10:1, otherwise I'd never close it!  I'm not THAT fit.  That 1-3/8" piston at 2kpsi equates to 3k pounds force on the piston.  If 10:1 MA near close, that's 300 lbs!  The math of multiplying the MA values in the system pan out. 

I know this has been beat to death on all forums in the past.  Even LD fell in this pit of lever madness. 

At any rate, when dealing with a series of levers in a chain to complete a task, their ratios are multiplied to find the end MA.

I'm interested in the lever you mentioned earlier.  Curious on its design.