Can we design an efficient dump valve hybrid?

[NCmountainShooter]

Sorry, once again, you totally lost me.... You need to draw it out and figure all the forces on all the moving parts, and if you are convinced it will work build one to see how well....

At stage 3, the middle chamber? at 0 psi isn't pushing back against the piston, so there is still 1/3 of the 2K force on the piston pushing it towards the VC....

The efficiency was never better than about 1.33 times what we can get conventionally at 2K, let alone at 3K.... so basically ANY wasted air makes it not worth the bother, IMO....

Bob

Regardless of the mechanism, can you run the numbers for what we could expect out of X volume of air at 6000psi followed by X at 2000psi? You'd need to know where the projectile will be when the pressure gets down to 2000psi to figure out from there what doubling the volume of air behind the pellet is going to do. If it takes a 45" barrel to get get full velocity out of that much air, then that would be good to know before pushing the design any further. You could use the numbers you quoted for the .308 with a 10.3cc valve at 6000psi and a 30cc valve at 2000psi for the dump.

[NCmountainShooter]

As an aside, where can I find Lloyd's internal ballistics spreadsheet you used to do some of your math?

[rsterne]

Here is a sketch of the basic idea using a stepped piston like that in a regulator, only acting backwards like a typical pressure booster.... Black lines are the stepped cylinder, blue the stepped piston, and red an airflow passage and check valve (located in the cone shape in the small end of the piston).... The 2K chamber on the left is supplied from the regulator.... The 6K chamber on the right is the firing chamber, vented by a dump valve to the barrel....



The dashed blue line is the piston in the compressed (firing) position (ie to the right), it is sitting up against the shoulder in the cylinder, (actually against a light return spring in the middle portion of the cylinder, not shown).... When the gun is fired, the 6K chamber drops to zero (guage), and the 2K cylinder at the left is full (up to the dashed line) with 2K air.... Because of the extremely short response time of the shot, I do not want the piston to move during the shot to cause any variations in velocity.... Since the pressure is so high (6K), even a small movement would make a big difference....

In order to move the piston back to the cocked (decompressed) state (ie to the left), three things have to happen....

1. The volume of 2K air in the low pressure chamber must decrease (note air cannot flow backwards into the regulator to accomplish this)
2. The pressure in the firing chamber must reach 2K
3. The pressure in the middle chamber must also reach 2K

Conditions 2 & 3 are required to equalize the pressure across the piston.... Condition 1 would be achieved by venting it to the port where the red arrow is on the top of the cylinder.... The air would flow into the middle portion (where the spring is) and through the piston and check valve into the firing chamber.... With equal pressure on both sides of the piston, the spring would recock it.... NO AIR IS WASTED IN THIS COCKING STROKE (the air simply moves from the left side of the piston to the right side, into the middle and firing chambers).... The passage between the low pressure chamber and the middle chamber would then have to be closed, and the middle chamber vented to the atmosphere.... The check valve in the piston would close and as the pressure in the middle chamber bleeds off, the regulator would top up the low pressure chamber, moving the piston to the right and compressing the air in the firing chamber back to 6K.....

The problem with this design is that the volume of 2K air used for every shot is the volume of the low pressure (left) chamber over the entire stroke of the piston.... which is 3 times what actually goes out the barrel.... 2/3rds of the air, all of the 2K air used to cock the piston in the middle chamber, is vented to atmosphere on the compression stroke.... Obviously, that is terribly inefficient, and renders the whole exercise useless....

Your task, should your choose to accept it, is to eliminate that wasted air.... *grin*

Lloyd's spreadsheet is proprietary, he was nice enough to give me a copy.... I don't have any way to superimpose two shot cycles as you suggest....

Bob

[NCmountainShooter]

Here is a sketch of the basic idea using a stepped piston like that in a regulator, only acting backwards like a typical pressure booster.... Black lines are the stepped cylinder, blue the stepped piston, and red an airflow passage and check valve (located in the cone shape in the small end of the piston).... The 2K chamber on the left is supplied from the regulator.... The 6K chamber on the right is the firing chamber, vented by a dump valve to the barrel....



The dashed blue line is the piston in the compressed (firing) position (ie to the right), it is sitting up against the shoulder in the cylinder, (actually against a light return spring in the middle portion of the cylinder, not shown).... When the gun is fired, the 6K chamber drops to zero (guage), and the 2K cylinder at the left is full (up to the dashed line) with 2K air.... Because of the extremely short response time of the shot, I do not want the piston to move during the shot to cause any variations in velocity.... Since the pressure is so high (6K), even a small movement would make a big difference....

In order to move the piston back to the cocked (decompressed) state (ie to the left), three things have to happen....

1. The volume of 2K air in the low pressure chamber must decrease (note air cannot flow backwards into the regulator to accomplish this)
2. The pressure in the firing chamber must reach 2K
3. The pressure in the middle chamber must also reach 2K

Conditions 2 & 3 are required to equalize the pressure across the piston.... Condition 1 would be achieved by venting it to the port where the red arrow is on the top of the cylinder.... The air would flow into the middle portion (where the spring is) and through the piston and check valve into the firing chamber.... With equal pressure on both sides of the piston, the spring would recock it.... NO AIR IS WASTED IN THIS COCKING STROKE (the air simply moves from the left side of the piston to the right side, into the middle and firing chambers).... The passage between the low pressure chamber and the middle chamber would then have to be closed, and the middle chamber vented to the atmosphere.... The check valve in the piston would close and as the pressure in the middle chamber bleeds off, the regulator would top up the low pressure chamber, moving the piston to the right and compressing the air in the firing chamber back to 6K.....

The problem with this design is that the volume of 2K air used for every shot is the volume of the low pressure (left) chamber over the entire stroke of the piston.... which is 3 times what actually goes out the barrel.... 2/3rds of the air, all of the 2K air used to cock the piston in the middle chamber, is vented to atmosphere on the compression stroke.... Obviously, that is terribly inefficient, and renders the whole exercise useless....

Your task, should your choose to accept it, is to eliminate that wasted air.... *grin*

Lloyd's spreadsheet is proprietary, he was nice enough to give me a copy.... I don't have any way to superimpose two shot cycles as you suggest....

Bob

Can you point me to a link where I can get a copy through appropriate channels or at least price it out, or is it proprietary as in secret? I certainly don't want to cheat him his due if he put the amount of work I suspect he put into that spreadsheet.

I'm curious if the superimposed shots would act like a single shot from a 60cc plenum that dumps at 4000psi or if it behaves completely differently.

Though I'm not good enough at the math to do the numbers, I suspect strongly that this can be done without venting the air. If half is boosted to 6k and half is left at 2k, so long as it all gets applied to the rear of the pellet I don't consider that a waste. Whether it is practical for a rifle or for an artillery battery is a different question.

The main practical question I have as to whether this is feasible or not is whether I can force 2k of air through a check valve with minimal external force. If that is possible, my design will work given a competent machinist and the right materials.

I will try to put all the pieces together in my design to draw and better explain.

[rsterne]

Lloyd's spreadsheet is basically not available, you would have to convince him you really needed it, and that he could trust you 110%.... I am not aware of anyone else besides me that has a copy.... As with all such things, it is a work in progress and a labour of love, and I think it is the feedback I provide him which made it available to me.... something I am grateful for nearly every day....

Using the example we are working with, 10.3 cc of 6000 psi air through a dump valve, the residual muzzle pressure is over 1300 psi (so the gun will be incredibly LOUD), and the pressure doesn't drop to 2000 psi until the bullet has already gone 17" down the 30" barrel.... By that time, the bullet has already reached 87% of it's muzzle velocity.... Although I can't use the spreadsheet to calculate what additional velocity one might gain by increasing the volume available at that point, all it could do is add more push during that last 13" of the bullet's travel down the barrel, by reducing the rate at which the pressure declines (ie increasing the muzzle pressure and muzzle blast).... That is assuming, of course, that you could open that second chamber completely and instantly, trying to flow it through a check valve in the remaining millisecond before the bullet exits the barrel ain't gonna cut it, IMO.... The critical part of the acceleration is the initial push of the 6000 psi, the part that could be influenced by a second chamber opening at 2000 psi (and 17" down the barrel) is VERY small.... The pressure as seen by the bullet would still be 6000 psi initially, 2000 psi at 17" down the barrel, and instead of 1300 psi at the muzzle, some value greater than that, depending on how large the second chamber was.... If that second chamber was 30cc, then the decay in pressure for that last 13" of travel would be from 2000 psi (in both cases) down to about 1560 psi instead of 1300+.... The greatest difference in pressure would occur in the last part of the barrel, where virtually no gains are to be made anyway.... I don't think that is a very efficient way to use air.... and in fact I'm not sure you would even see a consistent, measurable difference in velocity....

Instead of using a dump valve, closing the valve on the 6K chamber at the 17" point in the bullet travel would only lose 7 fps (~3.5 FPE) and yet would save fully 33% of the air inside the 6K chamber.... Once again, you can see why dump valves are a poor choice....

BTW, once the second chamber is dumped, the two valves together would act like a 40.3 cc valve at 3022 psi.... ( (30 x 2000) + (10.3 x 6000) ) / 40.3 = 3022....

Bob

[NCmountainShooter]

With the the amount of air doubled, couldn't we use smaller chambers for the same size projectile?

[rsterne]

As I tried to explain, doubling the amount of air when the bullet has already achieved 87% of it's velocity at 17" down the barrel will do virtually nothing.... However, cutting the volume of the 6000 psi chamber by 50% would drop the energy down from 224 FPE to less than 180 FPE, still using the 30" barrel....

Bob

[NCmountainShooter]

As I tried to explain, doubling the amount of air when the bullet has already achieved 87% of it's velocity at 17" down the barrel will do virtually nothing.... However, cutting the volume of the 6000 psi chamber by 50% would drop the energy down from 224 FPE to less than 180 FPE, still using the 30" barrel....

Bob

Is that 180fpe for just the 6000psi or both 2000 and 6000? Is it still going to be at 87% 17" with the smaller chamber?

[NCmountainShooter]

Regarding the mid chamber air, can we just move it back and forth between 2 chambers? If we had a check valve that could switch directions or two check valves going opposite directions that could be turned on/off depending which way you want the air to move. For instance if the mid chamber were compressed and allowed to vent through a check valve into a chamber with 0 psi, the next time we need to refill the mid chamber we just vent the air back from the other chamber through a check valve going the other direction. These could be controlled by a cover that slides back and forth between the two.  The other chamber would also need a piston working on it, but that's not difficult.

Edit to add picture. Pardon the bad art work.

Edit2: Looking at it on paper the issue seems to be that the rear chamber changes volume without changing pressure. Half of the difference is made up by filling the valve chamber from the rear chamber. That still leaves some displacement unaccounted for. This might work better if we only tried to compress 2 to 1. That means the torus of air in the mid chamber is equal in volume to the air in the valve chamber. As the piston moves to the rear, it forces air from the rear through a check valve into the valve chamber. As the piston moves forward it can pull more air from the regulator.

[NCmountainShooter]

Upon further review, this idea seems to work using 2 to 1 as the compression. I don't even think you have to have check valves between the two sides of the mid chamber. The divider just has to be slightly perforated. Because the mid chamber never changes volume, it's pressure doesn't have to change, just the relative position of the piston. The pressure pushing back on the piston also includes the area around the valve chamber, but this is vented to the atmosphere and doesn't add anything. So long as the regulator keeps filling up the rear chamber, we should still get effortless 2:1 compression. If we regulate that to 2500psi and compress up to 5000psi in the valve chamber, we should still get some considerable force and hopefully some good efficiency. Or if we want to run a 4500psi tank, we can regulate to 3k and still get 6k psi in the VC.

I'm not certain about perforating the divider or using reversible check valves. I almost wonder if the mid chamber is even necessary. With a check valve from the rear to the front chamber, if the piston moves back it just displaces the air from back into the front. Once you hit the rear of the stroke and close the check valve, as you push forward, the air from the regulator replenishes the rear and sends the piston forward. This could be completely automated with a light spring pushing the piston to the rear. The regulator may need to be blocked while the piston moves to the rear then opened going forward again.

Am I missing something here?

[rsterne]

Yep you keep missing that you have to have the same force on both sides of the piston to reset it for the next compression stroke.... Force = pressure x area.... If you just open a valve between two chambers of equal volume, one at 2K and one at zero, you get both at 1K.... the air doesn't move completely from one to the other, only half of it does....

The 180 FPE was just for the 6000 psi x 5.15 cc and the 2000 psi point would now occur earlier at about 8.5" down the barrel.... If you have the 2nd chamber dump at that point, you will get more out of it than before, the two chambers will work (from that point on) as if it was 20.15 cc at 3022 psi.... You will gain a few FPE instead of basically nothing, but you are still using a LOT of air to do it.... and your velocity is down 100 fps from your goal.... None of these dual chamber setups are as efficient as a straight 3000 psi conventional PCP with the valve closing at 50% (15" of travel)....

I have to tell you, I'm growing a bit weary of this.... You need to do some drawings and work out the math for each step and figure out how to move the piston without losing any air.... or it's a waste of time.... I'm going to take a break from this thread for a while and let you ponder it....

Bob

[NCmountainShooter]

Yep you keep missing that you have to have the same force on both sides of the piston to reset it for the next compression stroke.... Force = pressure x area.... If you just open a valve between two chambers of equal volume, one at 2K and one at zero, you get both at 1K.... the air doesn't move completely from one to the other, only half of it does....

The 180 FPE was just for the 6000 psi x 5.15 cc and the 2000 psi point would now occur earlier at about 8.5" down the barrel.... If you have the 2nd chamber dump at that point, you will get more out of it than before, the two chambers will work (from that point on) as if it was 20.15 cc at 3022 psi.... You will gain a few FPE instead of basically nothing, but you are still using a LOT of air to do it.... and your velocity is down 100 fps from your goal.... None of these dual chamber setups are as efficient as a straight 3000 psi conventional PCP with the valve closing at 50% (15" of travel)....

I have to tell you, I'm growing a bit weary of this.... You need to do some drawings and work out the math for each step and figure out how to move the piston without losing any air.... or it's a waste of time.... I'm going to take a break from this thread for a while and let you ponder it....

Bob

Thanks Bob, sorry for being a bother. I'll have to work on it some more as you say.

[rsterne]

Perhaps a totally different track?.... Don't worry about the efficiency.... Build the gun to use a 6K dump valve with a volume of 50% of the barrel volume.... Carry a 4500 psi Pony tank into the field, regulated down to 3000 psi and equipped with a 2:1 pressure booster (or the two combined into a regulated pressure booster if such a thing exists) so that it has a 6K output.... Use hoses and fittings, and a gun, designed to hold 6K in the valve.... Fill, shoot, and repeat....

The gun is a single shot, but it gets incredibly light, even with a 30" barrel, because it has no reservoir.... Using an 18cc dump valve at 6K should be able to push a 150 gr., .308 cal bullet about 950 fps (300 FPE).... The efficiency of the shot is 0.66 FPE/CI (better than most big bores) but when you include the air vented from the booster, it drops to about 0.44 FPE/CI, still in the range for many big bores.... You will lose some 6K air from bleeding the hose, though....

If instead of the dump valve you can control the dwell accurately using a balanced valve (so that the hammer energy doesn't get overwhelming) you can, of course, drastically increase the efficiency.... If you can close that same 18 cc valve when the bullet exits the muzzle you would have the same power, and the efficiency would be 0.98 FPE/CI.... Close the valve at 50%, the velocity only drops 20 fps and the efficiency jumps to 1.26 FPE/CI.... However, you have the added complication of filling the gun to exactly 6K for each shot.... although a smaller amount of air would be wasted by the (smaller) booster....

Bob

[NCmountainShooter]

Perhaps a totally different track?.... Don't worry about the efficiency.... Build the gun to use a 6K dump valve with a volume of 50% of the barrel volume.... Carry a 4500 psi Pony tank into the field, regulated down to 3000 psi and equipped with a 2:1 pressure booster (or the two combined into a regulated pressure booster if such a thing exists) so that it has a 6K output.... Use hoses and fittings, and a gun, designed to hold 6K in the valve.... Fill, shoot, and repeat....

The gun is a single shot, but it gets incredibly light, even with a 30" barrel, because it has no reservoir.... Using an 18cc dump valve at 6K should be able to push a 150 gr., .308 cal bullet about 950 fps (300 FPE).... The efficiency of the shot is 0.66 FPE/CI (better than most big bores) but when you include the air vented from the booster, it drops to about 0.44 FPE/CI, still in the range for many big bores.... You will lose some 6K air from bleeding the hose, though....

If instead of the dump valve you can control the dwell accurately using a balanced valve (so that the hammer energy doesn't get overwhelming) you can, of course, drastically increase the efficiency.... If you can close that same 18 cc valve when the bullet exits the muzzle you would have the same power, and the efficiency would be 0.98 FPE/CI.... Close the valve at 50%, the velocity only drops 20 fps and the efficiency jumps to 1.26 FPE/CI.... However, you have the added complication of filling the gun to exactly 6K for each shot.... although a smaller amount of air would be wasted by the (smaller) booster....

Bob

I think that is a very sensible solution that totally negates all the fun of figuring out the mechanics. I think using air to run the pressure booster can't be done without wasting at least the same as what you dump down the barrel. It just can't be done. It took your previous post and an epiphany to get that. What could be done is to combine the first idea of a lever and a pressure booster. Assuming a 2:1 booster with 1" diameter, 3000psi doubled to 6000psi, the pressure to lift the ring of the bigger diameter section is 2356lb. That's better than the 4712lb to compress the front chamber directly. If we use a hydraulic chamber instead of the air chamber to open the piston and fill the front chamber, when you release the hydraulic the piston will have its full 2:1 force to apply. What's the math on a 2356lb lever?

Edit:
Nix that. It's worse than on page one because the chamber volume is so much more. If we apply this back to the math for that first lever it would bring the 100lb weight to 50lb. Use 18" instead of 12", and it's 37.5lb. It's thus nonviable for big bore but a contender for 50fpe.

On your last post, I definitely want to understand balanced valves better but I'm nowhere close to that.

[NCmountainShooter]

OK, so before you start jumping off the walls, that is FAR from a dump valve, in fact the dwell is so short the valve is closing when the pellet has only moved less than an inch.... To get back to about where we were for power and efficiency, and with a dump valve, we need to reduce the plenum (in this case valve) volume.... I had to do some trial and error, but here is what I came up with.... It turns out you only need about 1/10th the volume, 1.67 cc of air at 6000 psi to get back to 50 FPE with a dump valve....

Regulated, compressed to 6000 psi, 1.67 cc valve with dump shot.... 50 FPE @ 1.29 FPE/CI.... So  the answer is yes, what you are proposing should work.... IF you can build it....

Unfortunately, that's a big IF.... You need to start with 5 cc of air (0.305 CI) at 2000 psi and then compress it 3:1 to 6000 psi.... Let's say that you use a piston 1/2" in diameter, which is 0.196 sq.in.... you need a cylinder 1.56" long, and a piston with a 1.04" stroke to increase the pressure 3:1....  At the end of the compression stroke, the force on the piston would be 1178 lbs. so you would need quite a leverage system to achieve that.... If the lever was a foot long, you would still have a 100 lb. load.... You could trade off smaller diameter for longer stroke, or larger diameter for less stroke on the piston, but you still end up with a 100 lb. load on the end of a 1 foot lever to compress that 5 cc of 2000 psi air to 6000 psi....

So the answer to your question is, yes, by using a much higher pressure you can make a dump valve as efficient as a conventional PCP.... The question then becomes, can you build and operate it?....

Bob

Going back to this post. Substitute 3000psi and 2:1 compression. Put a pressure booster between the lever and the chamber. Use 18" of lever. 37.5lb load on the lever is the end result. My umarex octane had a 50lb lever. If we work backwards from what amount of lever strength is tolerable we can figure out a max FPE for this system. 75FPE aught to get us back to 50lb on the lever.

[rsterne]

Starting with 3000 psi, you only need 3.34 cc of air, and compress it 2:1 to get that 1.67 cc @ 6000.... Assuming the same diameter (1/2") the load at the end of the stroke is still the same, but you only need half the stroke, cylinder is 1.04" long, stroke is 0.52".... Half the stroke means twice the MA, so half the force on the same length lever.... However, your starting load is greater than before.... Alternately, you can decrease the diameter and the loads, and increase the piston stroke, getting back to the same load at the end of the lever....

This is do-able, but of course you are talking wayyyyyyyy less power than the 224 FPE of the .308 cal.... 50 FPE using the numbers above.... Plus you need a source of 3K air, of course....

There is some info on balanced valves here in the Geek Gate.... they are in their infancy at the moment.... but show promise.... Basically a knock-open design with a balancing piston that removes the additional load of the air pressure holding the valve closed, just leaving the pressure times the stem area for the opening and closing forces.... requiring much less hammer strike....

Bob

[NCmountainShooter]

I want to correct my earlier statement that running the pressure booster can't be done without wasting the air. The only instance where I think you could get away with that mid chamber run by air is if you ran two pressure boosters side by side. They would need to alternate with one compressing as the other releases. Because there are equal forces in the two rear chambers they can push the mid chamber air back and forth. This is obviously not practical. You either run a double barreled gun with twice the weight or two pressure boosters for one chamber. It is quick on the follow up shot either way though.

[rsterne]

Sorry, I still don't see it.... When one booster is on the compression stroke, ALL of it's force is required to raise the pressure of the firing chamber to 6K.... There can be NO pressure in the middle chamber at max. stroke.... However, in the other booster, returning the piston to it's uncompressed position (against 2K pressure) requires 2K of pressure on both it's firing chamber (1/3rd of the area) and middle chamber (2/3rd of the area).... Connecting the two middle chambers together would see the volume move back and forth, but there would still be 2K of pressure in both middle chambers.... so no compression could occur....

In addition, the large (low pressure) side of the chamber that is on the cocking stroke is full of 2K air, which in my design would flow into the middle and firing chambers.... If the middle chamber is being filled by the air from the middle chamber on the other booster, then that excess air has nowhere to go.... unless you vent it....

BTW, in my suggestion of having the booster external to the gun, I realize that there is an air loss during recocking the booster, and mentioned that as a loss of efficiency.... The other alterative, of course, is to build a PCP that runs on 6K and figure out how to fill it safely.... There are big bores safely running 4500 psi now, it's only a matter of time before they go higher.... The problem currently is a safe way to store air at an even higher pressure to fill them.... or use a booster....

ob

[NCmountainShooter]

Sorry, I still don't see it.... When one booster is on the compression stroke, ALL of it's force is required to raise the pressure of the firing chamber to 6K.... There can be NO pressure in the middle chamber at max. stroke.... However, in the other booster, returning the piston to it's uncompressed position (against 2K pressure) requires 2K of pressure on both it's firing chamber (1/3rd of the area) and middle chamber (2/3rd of the area).... Connecting the two middle chambers together would see the volume move back and forth, but there would still be 2K of pressure in both middle chambers.... so no compression could occur....

In addition, the large (low pressure) side of the chamber that is on the cocking stroke is full of 2K air, which in my design would flow into the middle and firing chambers.... If the middle chamber is being filled by the air from the middle chamber on the other booster, then that excess air has nowhere to go.... unless you vent it....

BTW, in my suggestion of having the booster external to the gun, I realize that there is an air loss during recocking the booster, and mentioned that as a loss of efficiency.... The other alterative, of course, is to build a PCP that runs on 6K and figure out how to fill it safely.... There are big bores safely running 4500 psi now, it's only a matter of time before they go higher.... The problem currently is a safe way to store air at an even higher pressure to fill them.... or use a booster....

ob

Yup. I had to picture the two boosters back to back and balance the forces out that way to make sense of it in my head. You end up with 3k in one chamber trying to compress the other chamber to 6k, because the two middle chambers at 3k just balance each other out. Only if both chambers and both mid-chambers were open to each other could the piston move back and forth without effort. Because we're sealing one off and trying to double its pressure, we have to vent its mid chamber to balance the two sides. Bah.

[NCmountainShooter]

Since it seems I have to keep combining ideas to get better results, let's combine a double piston system and a lever to make up the difference in force. Instead of moving air back and forth, lets vent the mid chamber of one into the front chamber of the other and vice versa. Here is a simplified representation of back to back pistons and the extrapolation to how it might actually work side by side.

1) Start ready to fire one chamber. Open and close that valve.
2) One chamber is 0psi. Vent the other's mid chamber to this and they'll equalize at 2000psi between the compressed chamber and the other mid chamber. 
3) The piston hasn't moved yet. Run 3000psi to the mid chamber that needs to expand and apply force on piston to compress the other mid chamber's air into the expanding firing chamber.
4) You're ready to fire the other chamber now.

For a 1" diameter piston, 3000 to 6000 psi boost, I get 356lb 785lb of force required to compress the mid-chamber and firing chamber air from 2000psi to 3000psi. That's low enough to run with a 1' 18" side lever. This is for the 230fpe .308 at that.

Thoughts?

Edit: correction, the force difference should be 785lb.
(.25 x 3.14159 x 3000psi) - (.25 x 3.14159 x 2000psi).
Not as awesome but still doable with a longer lever.

Chris