Wonder why ????

[GadgetX]

Can someone explain in 2 sentences why a M-ROD shots increase FPS around 2200-2500 psi.  Seems that 3000 psi should be higher FPS. 

Seems like we need some kind of limiter at 2500 psi.   

Mike

[wilsonj1018]

because at the higher pressure of 3000 psi there is more pressure up againt the back side of the valve and the hammer strike cant over ride the 3000 psi as well as it does at 2500 psi. there i got it all in one sentence lol.

[GadgetX]

Thanks.   

[cactusrat]

Sentence #1 - It just does.

Sentence #2 - Like Wilson1018 said.

[bstaley]

Can someone explain in 2 sentences why a M-ROD shots increase FPS around 2200-2500 psi.  Seems that 3000 psi should be higher FPS. 

Seems like we need some kind of limiter at 2500 psi.   

Mike

Because that's what the current settings yield.  You could easily change that.

[Ribbonstone]

OK. Will try to explain it.

The force holding the valve closed vs the force opening the valve.


Holding the valve closes is the valve return spring (a minor player) and the air pressure acting on the valve stem.  Even if the valve stem is .3” wide, that works out to 210 pounds of force from air pressure alone.


Opening the valve is the force of the striker’s hit to the valve stem.


At high pressure, the closing force is pretty high.  Once smacked by the striker. the valve will open and close fast. That lets out a little “blip” of air, and the pellet is sent on it’s way at a lower speed.

BUT, each”blip” of air released lowers the air pressure in the air tube, which lowers the closing force to the valve. So each hit to the valve by the striker opens the valve a little more, and the pellet shoots a little faster.

At some point, the to forces are almost in balance and the gun shoots as fast as it is going to at that setting.

After that balance, the pressure in the air cylinder has dropped, and the opening force is greater than the closing force.  BUT the results is that the valve stays open longer, and most of that time spent open is after the pellet has already started its trip down the barrel.  Rather than a “blip” of air, are getting a long “burrrrp”, and velocity drops.

Increasing the striker’s hit to the valve (opening force) will make the balance point come at higher air pressure (closing force).  Decreasing the smack of the striker would lower the pressure of the balance point. 

[cactusrat]

Can someone define a sentence.

I seem to be confused.

(there’s the two sentence limit again)

[Ribbonstone]

Just one:

Foce holding vlave closed greater than opening force until closing force (pressure) drops.

[GadgetX]

A miracle.  I understand.  Thanks !!

Followup question.  Why don't AG makers use a regulator, say at 2500 psi on a second smaller chamber (tank) that preloads no more than best pressure.  That seems it would save air and get the shots more consistent on the top.

Mike

[cactusrat]

That's what a regulator does on the air tube.

No need for a second tank/chamber.

(there’s the two sentence limit again)

[GadgetX]

What I am saying is if the AG is shot with a 2nd fitted tank which is filled by a connected large tank.  The large tank may may have 3500 psi, but the smaller tank is never over 2500 psi because of a regulator, you would never shot over 2500 psi, the ideal pressure.

[cactusrat]

Okay, I see what your saying. That’s something like shooting tethered to a scuba/scba tank, but with a regulator in between the tank and gun.

Yes it would work. But only off a bench. Just thinking a scuba tank strapped to my back with a 6 foot hose attached to the gun walking threw the woods gives me a headache.

Oh my, I used more than two sentence limit.

[Rescue35]

That is exactly how the factory guns that include regulators work. Also the aftermarket regulators for the Marauder etc.

The reason ALL of them do not have regulators is cost. Especially since you can tune them to semi-regulate themselves by shooting through the sweet spot.

[GadgetX]

THE COST.  Now it is becoming clear.  Wonder when someone will come out with a optional regulated tank setup for the M-Rod?  Can some name a few AGs which have a regulated tank system?  Is there a self contained aftermarket regulator for the M-Rod?

Mike

PS - Sorry that was 5 sentences ....   

[Rescue35]

Some of the FX and Daystate line are regulated IIRC. The RAW is also. There is (was?) an aftermarket regulator for the MRod. Motorhead is running one and has a very extensive thread here in the PCP gate about the work he did to convert it.

[Bill G]

Yes, Most are drop in units.  One of the problems with a regulator is, not every one wants to shoot the same FPE output.  This can also be exacerbated by the valve mods.  The better a valve breaths the lower you can have the set point.  Higher FPE tunes require a larger section of regulated air supply.  This makes for a smaller high psi reservoir.  Also, the more reliable regs have vent holes in them to insure that the chamber that contains the disc springs can maintain nuetral pressure.  That vent hole has to vent to atmosphere.  This means that you have to drill a hole in the resivior tube in the general vicinity if the vent hole in the reg.  The placement will vary from one gun to the next dependant upon the FPE you want to shoot.  The plenum has to be able to deliver the reqired air with an acceptible pressur drop across the valve or effieciency dies.  Low efficiency is counter productive to why you wanted a reg in the first place.  Also, as Scott has pointed out, the hammer weight on a reg'ed rifle is probably too high to maximize effieciency.  There is a bit more to a reg than droping it into a rifle and a golden aura envelopes you and the gun allowing ultimate greatness in PCP airgunning.  Basicly you have to have settled on a power range.  Too low and you can't go higher and too high there CAN have deminishing returns from having a smaller high PSI reservior.  As with every aspect of PCP airguns, it is give and take.  It require some pontification.  I have been building and experimenting with regs for a while now.  I have attempted to build un-vented models but they all tend to fail much earlier than vented ones.  With moving parts, they will all fail eventually.  I only have the .25 marauder and it is such an air hog that regulating it has no real place.  The rifle can be tuned to have a 10fps ES at high power, lower shot count tunes.  With a reg, the count tends to be nearly the same.  The real benifit for a .25 is to let the rifle breath better, especially if you are wanting more FPE.  I'm currently working on some now but they are not for sale.  I will not sell something that I am not confident in yet or can not reasonably meet demand.  Perhaps in the future.

Bill

[cactusrat]

THE COST.  Now it is becoming clear.  Wonder when someone will come out with a optional regulated tank setup for the M-Rod?  Can some name a few AGs which have a regulated tank system?  Is there a self contained aftermarket regulator for the M-Rod?

Mike

PS - Sorry that was 5 sentences ....   

I don’t think a tank like that will sell.

Put a $500 regulator in the gun or buy a $1500 tank. (the prices are just to make a point).

(wow, stayed within the limit)