Limited Pressure Drop (LPD) Design

[SSCBen]

EDIT: This thread was split from its original thread to preserve the initial thread's subject while offering room to explore this new topic.

There's this thread where I detailed the concept with some calculations that are approximately valid. I should get the the adiabatic pressure ratio equation up because it's much more accurate, but what I have listed there should be approximately correct.

If you increase the air-water ratio in an air pressure water gun, the pressure will drop less. The LPD approach takes advantage of this fact by changing the geometry so that the air-water ratio is higher.

[isoaker]

Oh... basically, the LPD design is akin to using an Aqua Master Pre-Charger gun, prepumping a lot of air into the back side, and only pumping a much smaller volume of water into the front side such that the water does not experience a dramatic loss of pressure as it shoots out the nozzle while the air chamber expands. Makes sense, but requires a rather large chamber if you also wish to have a large firing volume available. From my understanding, then, the AquaMaster Pre-charger line would be categorized as an LPD design so long as one never pumps in too much water into the front side of the chamber. While their max pressures may not be as high as some may desire, the idea is there.

[HBWW]

Yes, the concept and operation are essentially the same, but in larger LPD systems, the air chambers are usually seperated from the water chamber to conserve space, which are then connected by piping. As for costs and manufacturing practicality, I think its very well possible to be done on a stock gun. The chambers could be similar to, say, the SC 400's reservoir in terms of material and size. This would offer about 700mL of water capacity in the PC yet still be compact enough to fit in a HydroBlitz. With some more scaling down, perhaps combining the air chambers into one oddly shaped chamber, I believe it could fit in a case with the same volume as the Orca, or even the Piranha.

As for costs, I believe those can be minimized with smart design, such as not having the end of the PC go through a maze of pipes before it reaches the valve and nozzle, placing the parts around effectively, etc. Unfortunately, the economy seems to be a limiting factor in materials right now, given the fact that SS hardly released anything last year and didn't for this year, as well as BBT's smarter designs to conserve material.

[isoaker]

I did a little more thinking regarding this type of blaster. While it makes perfect sense in terms of how it works, based on the difficulties encountered already with the Water Warriors Aqua Master Pre-Charger series, I don't foresee it being useful for stock blasters for awhile. If one increases the pressure in the back-side air chamber, the blaster would be extremely difficult to pump manually. It'd either require a very strong person or pump volumes to be reduced significantly that it'd get annoying. Larger LPDs really appear to need either an air compressor or compressed-air canisters if higher pressures are desired. If one is simply considering increasing the PC in an Aqua Master-type blaster, but not increasing the maximum PC pressure, while you'd get longer shot times, overall stream power wouldn't be any better than what was previously available.

For now, I can only conclude LPD systems shall remain in the realm of homemades until certain other restrictions (i.e. acceptable selling price for water blasters and certain safety concerns) become less restrictive.

[HBWW]

Well first of all, you can limit the pressure in the air system if pumping becomes too difficult. (I had a little idea of having a Supercannon II combined with a normal gun's pump systems, where you'd shoot the blast at high pressures, then press on the valve to depressurize it to pumpable levels) The only main manufacturing issue with LPD's would be the piston, given that was the problem with the pre-chargers. High pressures on LPD's are not really necessary and probably wouldn't be possible in stock guns due to their use of weaker plastics.

However, at the lower stream pressures, they probably might as well be using CPS or Hydro Power. LPD is just another option out there that can be scaled down from homemades to work for stock soakers, and if the piston can be worked out, the whole thing isn't difficult to implement. A valve for a bike pump, in fact, may be the best necessary for the air pump if the standard pump doesn't work for air.

[Silence]

iSoaker, the maximum pressure is the same, but the minimum pressure is increased. The attached diagrams are a rough estimate of pressure vs. time as you pump.

[isoaker]

@Silence: I do understand the idea behind the LPD design; the system is designed not to let pressure drop below a certain level by the time the water runs out. However, from Ben's original thread, he was referring to creating an LPD from his Supercannon 2 design. If you create an LPD system using the inner workings of a blaster like the Water Warriors Krypton, unless you increase its maximum pressure, you're not going to get better stream performance. The Aqua Master PreCharger system can already function like an LPD system if you don't pump in too much water into the front side. However, as soon as you start increasing the allowable max pressure in the air-chamber-side of the system, you'd got a major challenge when it comes to trying to pump in water. If one does as C-A_99 suggests and reduce pressure while pumping in water, that makes it easier to pump water, but then makes it more complicated overall to get the blaster fully charged.

[HBWW]

Well the point is to get the air chambers charged to the desired level before pumping in water. After that, water is pumped in. (being low dropoff, the pumping difficulty is not much harder when the water is nearly full, thus discharging air while pumping is unecessary and actually counter-productive unless you happen to put in too much air) If you want very high level performance, you would pump the water in before adding any pressure, then pressurize it above water pumpable levels. Since you'll probably be well in battle at the time, you'll have to then depressurize the air chamber enough so that pumping in water will be manageable. Either way, you're just trying to set it to a good balance between what you can pump and what power you need. Nozzle selectors are pretty much a must for these systems.

However, I don't see stock soakers allowing such high pressure levels; allowing pressure levels to go above whats pumpable with water. (since higher level pressures require more expensive materials to keep them safe) In essence, a stock LPD system would be used much like a pre-charger, unless the design calls for the user to use a bike pump to pressurize the air chamber. Either way, there would be a PRV on the air end to keep it safe, while the water pump would turn rock-solid if theres a limit to the water volume that can be pumped.

As for the WW noble gases, even if you don't try to limit water to LPD levels, you still don't have a reasonable amount of capacity to soak with since none of them offered sufficient PC sizes.

iSoaker does have a point though. Some people are going to buy an LPD gun only to realize that they don't have a bike pump, or more likely, are going to leave the system pressurized when in storage, though thats not much different than storing a fully charged CPS anyway. On the other hand, there have already been many user-unfriendly guns out in the market, such as the Arctic Shock and Overload, whose small PC's absolutely require that they be pre-charged with air so they get more than a squirt gun's worth of range. Personally, the only issues I see with stock LPD's are manufacturing and the fact that CPS does the same job just fine. (though its power is not as customizable without the use of balloons or tubes, heheh.) But until the patents clear, LPD offers a good option for high, customizable power, and still allows for very good PC volumes. The dropoff seems to be roughly the same as CPS and is most likely less than that of Hydro Power.