[Expert advice] Choosing a foam gun for PU foam sealant

The range of foam guns on sale is huge. Prices differ by a factor of tens: the cheapest cost a few hundred rubles, the most expensive a few thousand. Let us look at the parameters and properties worth paying attention to when choosing a gun.

Ergonomics
Probably the first thing to look at. A professional installer spends a lot of time with a gun in hand, and whether it is comfortable to work with affects both output and fatigue. So the first step is to pick the gun up and judge how comfortable it is to hold, how convenient the adjustment screw is, and how soft and smooth the trigger travel is. Comfort should be judged not only with bare hands but also in thick gloves — in winter there is no working without them.

Body material
Anything can happen on a site: the gun may be dropped or stepped on. For strength and reliability a metal body is preferable — it is stronger than a plastic one. Plastic guns, however, are usually lighter than metal ones, and for some users that is the deciding factor. A good compromise between strength and weight is a gun with a metal body and a plastic handle; there are plenty of such designs. A gun with a plastic trigger should be ruled out outright — it will not last long.

Polishing and PTFE coating
The better the finish of the gun's internal surfaces, the better the foam it produces. The inside should therefore be at least polished, and better still coated with PTFE (Teflon). The outer surfaces matter too: foam residue and other contamination are easier to remove from a smooth surface, so it is good if they are polished as well, or PTFE-coated.

Tightness of the valves
A gun has two valves: a ball valve where the can is attached and a needle valve in the barrel tip. There is also one moving seal at the rear of the barrel, where the needle meets the trigger. Performance and service life depend directly on how tight these are, so it is better to check the valves and the seals either before buying or immediately after, before the gun is put to work. It is easy to do: screw a can of cleaner onto the gun, run a little cleaner through it and unscrew the can. Then listen for leaks at the valves or at the needle seal — if they are not tight, you will hear a characteristic hiss. Better still, leave the gun with the cleaner can on it until the next day if you can, then pull the trigger and check whether the gun has held pressure. If it has, all is well; if not, the gun is faulty and is best returned to the seller.

Serviceable or sealed design
If foam has cured inside a gun that cannot be taken apart, there is no way to remove it and the gun has to be thrown away. A serviceable gun can be dismantled, cleaned and brought back into working order. With a new or lightly worn gun that may well succeed; with a heavily worn one it most likely will not. Either way, a design that can be taken apart is preferable to a sealed one.

Expansion chamber
The expansion chamber has a direct effect on the quality of the foam: the larger the chamber, the better the foam. Whether a gun has one, and how big it is, is easy to tell by the thickening at the base of the barrel. Other things being equal, a gun with an expansion chamber is the better choice.

Removable barrel tip
Most gun models come with a removable tip on the barrel, but there are designs without one, and their barrel is usually thinner. Each design has its supporters. A gun with a thin barrel is more convenient for filling narrow gaps, for example around door frame extensions. With a removable-tip gun you have to fit the special plastic straw supplied with it for such work. On the other hand, a removable tip can be unscrewed and cleaned when it gets clogged, restoring the gun to working order.