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This thread is under construction. Probably worth reading, but it's not comprehensive. Welcome to the High Pressure Air (HPA) FAQ. Here we'll be covering the basics of what HPA is, what it's advantages are, how to find out if HPA is for you and how to shop for HPA products. If you're wondering about getting into HPA for airsoft then please read the entire FAQ before asking questions - this will save yourself and other forum members a lot of time and effort. At the bottom of this post you will see when the FAQ was last updated. What is 'High Pressure Air' (HPA)? Introduction In a nutshell, HPA works through the controlled release of compressed air. In an AEG you can expect a gearbox to actuate a piston which in turn compresses air that's released down the barrel to project your BB. In a green gas, duster or CO2 airsoft gun this gas is stored in a compressed state within a vessel and expelled down the barrel to project your BB. In a spring airsoft gun the potential is stored in a spring that actuates a piston, compresses the air inside the cylinder that's in turn pushed down the barrel to project your BB. In HPA the concepts are very much the same: Like green gas, duster or CO2 the gas is stored pre-compressed and many pneumatic HPA engines function very similarly to gas blow back rifles - indeed, in many cases HPA can be used to power a lot of existing GBB and GBBRs (more on that later). Table of contents 1. Power sources 2. Your HPA 'rig' 3. 'Kits'/'Engines', 'Guns' and 'HPA Tapped' 1. Power sources To understand what HPA is, you must first know how 99% of guns in airsoft are powered so that you know what HPA is not: Electric AEGs (Automatic Electric Gun) AEPs (Automatic Electric Pistols) Green gas, duster and CO2 GBB or GBBPs (Gas Blow Back pistols) GBBRs (Gas Blow Back rifles) NBB (Non Blow Back) Spring HPA Electric solenoid engine Pneumatic engine 2. Your HPA 'rig' As we've already covered, HPA is compressed air that's released in a controlled fashion to propel your BB. Think of it as the power source for your gun, but not what's inside the gun itself. It's akin to a battery (like an AEG) or a magazine full of green/duster gas (GBBP/GBBR). A typical HPA rig (i.e. all the functional exterior parts that a user needs to combine for their HPA powered gun to work) is comprised of three separate parts: The 'bottle', the 'regulator' and the 'line'. Not all HPA setups work with identical rigs, but this will become apparent later. For now, here's a nice picture of a typical HPA rig: Bottle This is where the air is store in a highly compressed state. There are two different types of bottles that you can buy, rated for two different pressures: 3000 psi (pounds per square inch) (206 bar) and 4500 psi (310 bar). 3000 psi bottles tend to be made from aluminium whilst 4500 psi bottles are almost always made from carbon fibre. Generally the shape of a bottle gives away its pressure rating as the more rounded corners of the 4500 psi bottles have a distinctive silhouette versus the more square edges of a 3000 psi bottle. Airsoft HPA bottles are identical to paintball HPA bottles. Every tank also has a 'bottle regulator' that comes with the bottle and steps down the output of the bottle so that the actual regulator can deal with the incoming flow. This generates some complex issues that will be revealed later on as some bottles output at what is called 'Super Low Pressure' (SLP) (approximately 300 psi) whilst the rest tend to output from 450 psi to 950 psi. Different regulators work with different input pressures, so not all are happy with receiving the lower pressures from SLP bottle regulators. Bottle size is measured in ci (cubic inches). Bottles range from 13ci to 100ci, though most bottles sit around the 40ci to 70ci mark. Obviously a bottle at 4500 psi will go for longer than a 3000 psi bottle of the same size/internal volume. The bottle regulator also has three key features: The first is that it has an interface with what is called the ASA on the regulator or line (if you're using a 3000 psi rated line) - these threads on the top of the regulator also have one of two seals at the top to ensure a proper air-tight system. The second feature is refilling: A standard paintball fill nipple is present on most regulators and can interact with the machines in paintball and dive shops as well as with 'fill stations' (more on fill stations later). The third and final feature of most good bottle regulators is burst disks: Burst disks are a key safety feature that allow the tank to do an emergency, controlled venting of air if it's overfilled or there's a failure in the bottle regulator causing too high a pressure to be sent to the rest of the HPA system. HP burst disk: A higher rated burst disk that blows if the tank is overfilled. 3000 psi and 4500 psi tanks tend to use 5000 psi and 7500 psi HP burst disks respectively. LP burst disk: A lower rated burst disk that blows if the tank is outputting a pressure higher than it should be that would otherwise damage your gun or regulator. In both cases the burst disks aims to safely vent the air rather than the tank or entire hpa rig just continuing to fill with air that it's not built to handle and exploding. Click the spoiler to see some pictures of bottles and bottle regulators Regulator The regulator has two main functions: To further step down the pressure of the air to a usable psi and to do so in a way that means - during intense use - the gun doesn't get 'starved' for air. This latter point is sometimes called 'refresh'. Regulators with a higher refresh rate are more desirable as they can power air-hungry guns that would be otherwise starved by lower refresh rates. The regulator also acts as a hub for the line. Some regulators only have one possible output, whilst others have many. Some have the capacity for QDs (quick disconnects) which allow the user to rapidly disconnect the line for freedom of movement or modularity without compromising the pressure inside the regulator. Almost all HPA rigs have one or two QDs (usually one at each end of the line). Most regulators are easily adjustable between a range of outputs. This varies depending on the make of the regulator, but most airsoft regulators are designed to work between 30 psi to 160 psi. Click the spoiler to see some pictures of regulators Line The line is an air hose that connects the gun to the regulator. These come in many different forms, but most are between 24" (50cm) to 46" (116cm) long and have varying inner diameters between 3mm to 6mm. Most airsoft lines are rated for use up to 200 psi though some can handle up to 3000 psi. This is because some guns use an internal regulator and so the air hasn't been de-pressurised. More on this later. Some lines are coiled, some are braided and others are just normal looking rubber tubing. The most typical airsoft line will be 36" (91cm) long, have an inner diameter of 6mm, can withstand up to 200 psi and will be braided. Click the spoiler to see some pictures of lines 3. 'Kits'/'Engines', 'Guns' and 'HPA Tapped' Now that you know how HPA is 'powered', you must understand what this means on the gun side. How do we turn that air into propulsion for the BB? The following table of brands/products is more of a glossary to help you understand what people are talking about when they refer to the various HPA setups and we'll go into each one next. Note that 'Kits' and 'Engines' tend to be interchangeable vocabulary in most settings: Kits/Engines Electric solenoid Wolverine (Inferno, Hydra, Bolt etc.) Polarstar (F1, F2, Fusion etc.) ProTech (Mk1, Mk2 etc.) Fully pneumatic Daytona Gun Escort Sun Project 'Guns' Tippmann 'HPA Tapped' Due to the nature of this category, there are no specific brands/products related to it but we'll come to that You may remember in section 1. seeing 'electric solenoid' and 'fully pneumatic'. These are generally both referred to as 'conversion kits', 'engines' or simply 'kits' as both are drop-in replacements that require a 'donor gun' (i.e. an existing AEG or GBBR that one strips out and replaces the internals of) whereas 'guns' I'm here using to encompass the Tippmann M4 as - at the time of writing - it's the only HPA-specific gun that requires no additional modification to run on HPA. It has some rather specific quirks as well so I've given it its own section.