Thread from the WWn Wiki - originally developed by iSoaker and Andrew
3.1 Standard APH
4 Design elements
4.1 Standard APH
APH Compared to Hydrocannon
An Air Pressure Homemade (APH), can refer to any homemade water blaster which utilizes air pressure to power a stream of water. However, it is most commonly used to refer to traditional separate air chamber designs that use vertical water vessels, based on the XP Super Soaker designs. This design is very popular, combining high performance and design flexibility with low cost materials and simple construction. It is recommended for enthusiasts who have some experience modifying or repairing water blasters. Properly constructed, an APH can prove to be a powerful and effective addition to a water warfare arsenal, and if properly built and used, will outperform any manufactured water blaster.
The first recorded construction of an APH was Pepper's water gun. Built in 2003, Pepper's water gun featured several innovative design elements which later became standard in common APH-design. These included separate Pressure Chambers, an on-board reservoir, and interchangeable nozzles. This water gun also featured a homemade pump and pump-seal. In 2004, a consolidated version of this gun appeared in Ben's APH-design. This design is credited with popularizing the APH model and paving the way for a slew of homemade APH-designs to follow.
In 2006, a new type of CPH was created, the Constant Air Pressure Homemade (CAPH) in the form of SuperCAP, once again by Ben. SuperCAP relied on two pressure chambers, and a pressure regulator to keep the pressure almost constant. The larger of the two pressure chambers was filled with pressurised air and the second tank was filled with water. A regulator connected the two tanks together, keeping the pressure of the water chamber constant.
 Standard APH
Aph Firing Steps
The Air Pressure Homemade operates on the principle of air-pressure. During the first stage of operation, the rigid chamber is filled with air at room temperature and pressure. An inlet and outlet exist, and the outlet is closed. During the second stage of operation, water is drawn into the pump through the first check valve. During the third stage of operation, the pump is retracted, forcing water through the second check valve and into the rigid chamber. The air in the chamber will rise above the water as it is much lighter, and this orientation will be preserved normal to the direction of gravity (it is for this reason that most APH designs do not work when inverted. As the volume of water increases, the air pressure above the water increases because the air is much more easily compressed than the water. Eventually a maximum pressure will be reached. This pressure will be dictated either by the strength of the input force or by the tensile strength of the chamber material, whichever is lower. During the fourth stage of operation, the outlet is opened and the air pressure above the water forces the water from the chamber. As the volume of water decreases the air pressure decreases, and so the stream will become weaker the longer the outlet is open.
Air Pressure Homemades offer many advantages over stock or alternative homemade designs. They are generally more powerful than stock blasters because they lack a pressure relief valve and are constructed from sturdier materials. Depending upon the size of the pressure chamber(s) and the nozzle, an APH may also exhibit remarkably longer shot times than stock blasters. Finally, the simple construction and lack of complex moving parts makes a basic APH-design much more durable and reliable than stock blasters.
Air pressure's primary advantage over bladder pressure (CPS) is that it is easy to adjust and vary in power simply by controlling the amount of air being pressurized. This flexibility makes it easy to build very powerful designs.
Disadvantages to this design are often dictated by the physical limitations of the pressurization. APHs tend to be top-heavy given their long, cylindrical, top-mounted pressure chamber(s). The APH-design exhbits limited effective-shot time, as the range will fall off as the stream gets weaker. In addition, the decay of power over the duration of the shot can result in inconsistent stream lamination. Finally, APHs are not very efficient; a percentage of the water may remain trapped behind the nozzle near the end of the shot when air pressure is weakest.
The primary disadvantage to air pressure as a whole is that it requires more materials overall, as well as space. To solve some of the problems of the traditional APH, more air volume must be given which also involves more pumping especially as the volume increases.
CAPH Firing Steps
The Constant Air Pressure Homemade (CAPH) operates on the principle of air-pressure, just like the APH. However, unlike the APH, the CAPH uses a regulator to maintain this air pressure to keep the pressure in the water chamber constant. First the smaller pressure chamber is, almost completely, filled with water. Then the larger pressure chamber is filled with air and pressurised to around 100psi. The regulator is set to around 70psi, and transfers pressurised air, from the larger pressure chamber, to pressurise the water in the second chamber to 70psi. Whilst firing, the water level decreases and pressure in the second chamber reduces. The regulator transfers more pressurised air into the second chamber to maintain 70psi pressure on the water. Once the pressure in the first chamber falls below 70psi, the regulator stays open and the two chambers decrease in pressure together.
The CAPH design retains many of the advantages of the standard APH, with the addition of constant pressure. In fact a small and lightweight, yet practical CAPH system would be regarded by many as the ultimate water blaster.
A CAPH is usually quite large and heavy, and can be very expensive to construct. Also, unless there is some form of seperation between water and air, the CAPH cannot be fired upside down, or at some angles unless fitted into a backpack system.
Like a pressurised reservoir weapon, the CAPH water reservoir cannot be opened until the system is depressurised. Also refilling can take a long time, and requires a compressor to recharge the primary air pressure chamber.
 Design elements
 Standard APH
An APH is composed of three main sections which are the pump, the pressure chamber, and the reservoir. A check valve is placed between the reservoir and the pump and also between the pump and the pressure chamber. A trigger valve is placed between the pressure chamber and the environment. The orientation and positioning of any of these sections is flexible as long as the oulet in the pressure chamber is located at the "bottom" of the chamber.
The CAPH is composed of three main sections. These are; the larger primary air PC, the smaller water PC, and the regulator between the two. Like the APH the orientation and positioning of any of these sections is flexible, and the oulet in the smaller water pressure chamber must be located at the "bottom" of the chamber, unless a there is a separation between the air and water in this chamber. If there is a separation then it is possible to position the PC, the outlet valve and the nozzle inline with each other to make the flow more laminar.
APH Firing Steps