How to use a foam gun

Recommendation points

• Pistol design, principle of operation
• Connecting and replacing the cylinder
• Foam pressure adjustment and seam filling
• Using replacement attachments
• Flushing, maintenance and storage

If cylinders with a tubular nozzle are well suited for one-time work, then with frequent use of sealant, you should learn how to use a special dispenser – a gun for polyurethane foam. To do this, you need to know their structure and principle of operation, as well as be able to use and maintain the tool correctly..

Pistol design, principle of operation

The story about polyurethane foam guns should begin with the fact that these tools are collapsible and non-collapsible. This factor does not affect the device and the principle of operation of the mechanism, but directly determines the maintainability of the tool.

The base of each pistol is a grip body. It has a one-piece design with an adapter for connecting to a cylinder – a threaded ring located in the upper part. At the front of the handle there is a threaded nut into which a tube or pistol barrel is screwed. The key difference between non-separable modifications is that instead of a threaded connection, this unit uses a press fit.

1 – outlet valve; 2 – trunk; 3 – inlet valve; 4 – adapter for cylinder installation; 5 – trigger mechanism; 6 – an adjusting screw (latch); 7 – gun handle for polyurethane foam

At the end of the barrel there is a nozzle connected to the trigger mechanism by a rod – a thin spoke running along the entire length of the barrel. There is an adjusting screw at the back of the handle to limit the trigger travel.

The principle of operation of such a mechanism is based on two ball valves. When closed, the trigger return spring reliably locks both valves, preventing the advance of the polymer composition along the inner cavities of the pistol. When the trigger is pulled, both valves are opened: first the upper one, which ensures the flow of foam into the guns, and then, with a slight delay, the ball is removed from the seat of the front nozzle, so that the foam can freely come out. The shape of the seat is tapered, thus, the stronger the stem carries the ball, the larger the nominal diameter of the stem and, accordingly, the stronger the foam pressure.

Dismountable gun for polyurethane foam

The difference between a cheap tool is the absence of a top valve, so the working pressure of the cylinder always acts inside the tool. Also, the characteristic features include:

• using plastic instead of metal for the case;
• lack of precise fit and fit of balls in the seats;
• no polishing or Teflon coating of surfaces in contact with the foam;
• Leakage of the stop rod and screw, as well as the trigger mechanism.
• the absence of a “dead” position of the adjusting screw, in which the valves are closed not only by a spring, but also by tightening the thread of the limiter.

Connecting and replacing the cylinder

Polyurethane polyurethane foam has an atmospheric curing principle and requires air and moisture to cure. Thus, while maintaining the complete tightness of the pistol and the place of its connection to the cylinder, the composition in the internal cavities will retain the same properties as inside the factory packaging..

Before connecting the cylinder to the gun, you need to make sure that the seat in the adapter has no contamination in the form of foam, dust and small debris, the metallic sheen of the ball in the upper valve should be clearly visible.

Before connecting the cylinder, put it on the floor in an upright position and wait 2-3 minutes for all the liquid composition to collect at the bottom. Without changing the position, the gun is screwed onto the cylinder from above: it is important to get into the thread pitch so that the container with the foam becomes without distortion. As the screw is screwed on, the stop on the valve branch pipe will push the tubular spout of the cylinder and the built-in valve will open in it. Without turning the gun, you need to slightly press the trigger: the flow of compressed gas from the nozzle indicates that the gun is not clogged and is ready for work.

Unfortunately, the valves built into the cylinder often get stuck. From a purely technical point of view, it is possible to remove an unused cylinder from a pistol, but this can be done in about two cases out of three. Thus, before removing the cylinder, it is advisable to use it completely and make sure that there is no liquid foam left inside..

To remove the cylinder from the pistol, it must be placed vertically on the bottom so that the pistol is upside down. While the remaining foam flows down, you need to prepare a trash can or bag, as well as a cut of unnecessary rags. After a few minutes, you can try to remove the cylinder by wrapping a rag around the adapter and lifting the cylinder, unscrewing it. Beforehand, it will not be superfluous to press the trigger several times to blow out the foam from the gun with the rest of the compressed gas. If an intense hiss is heard when unscrewing the cylinder, it must be quickly screwed back and placed in a bag or bucket: after the final removal of the pistol, there is a high probability of foam coming out under high pressure.

Foam pressure adjustment and seam filling

Before you start working with a foam gun, you need to adapt to its throughput and adjustment features. It is recommended to select an irrelevant section of the joint and partially fill it, starting with the lowest feed, gradually unscrewing the adjusting screw. It is very important that the foam enters the seam evenly and at the same time at such a speed that the gun can be confidently controlled..

Fill horizontal seams in any direction, vertical seams from bottom to top. Sometimes it makes sense to zig-zag the nozzle so that the foam bundle sticks to as many surfaces as possible. With variable seam thicknesses, the foam head can be adjusted on the fly by pulling the trigger and, if necessary, by the stop screw.

Do not neglect the preparation steps before filling, i.e. priming and dusting. It will also be very useful to spray the joint with clean water from a spray bottle and wait about a minute until the surfaces are well moistened..

Using replacement attachments

For filling seams of complex shape and considerable depth, it is possible to recommend the use of interchangeable nozzles that fit over the nozzle tip. There are three types of these devices: silicone flexible hoses, rigid transparent tubes and conical tips..

Rigid tubes are used exclusively as extensions when the length of the gun barrel is not sufficient to fill deep cavities. Flexible hoses are used in cases where the seam has recesses and grooves of complex shape that require filling, while the rigid barrel of the gun does not allow turning the tool in the desired direction.

Tapered nozzles are used to give precise direction to the flow of foam at a minimum head. Typically, such nozzles are used when filling very thin seams, for example, in joints of sheet materials or for gluing various types of overlays. All tips described are disposable and not designed to be cleaned for reuse.

Flushing, maintenance and storage

After using the gun, turn the adjusting screw as far as it will go so that the trigger has no free play. The gun must be stored upside down between work, that is, the cylinder is installed on the bottom..

Practice shows that a quality pistol with a cylinder when assembled can be stored for several months. Nevertheless, this mode of using the tool is not welcome: the slightest gap in the body or connections is enough for the foam to gradually set, which for a pistol in most cases is a direct ticket to the trash can.

With dried foam inside the gun, clean is significantly complicated:

The technology of using polyurethane foam involves disconnecting the cylinder in cases where the break between work is at least a day. In such situations, the balloon is removed, keeping all precautions. If a hiss is heard during the twisting of the adapter, the cylinder is returned to the gun and further guided by considerations of economy. If there is little foam in the cylinder, it is better to release it in a controlled manner and dispose of it after hardening, so as not to damage the finish and property at the facility..

Before long-term storage without a cylinder, the gun must be flushed, for which use flushing liquid cylinders with a similar installation method. Before flushing the cylinder, it is recommended to blow off excess foam with residual compressed gas. After that, the tool is returned to the working position, the liquid is launched into the gun by a short pull on the trigger and left for a few minutes. Then the dissolved substance is released outside by feeding a new portion of the cleaner. The operation is repeated until the leaving composition is clean without the slightest traces of dissolved foam. Before placing the instrument in the box, it is necessary to remove the residues of dried foam from its outer surfaces, for which solvent 646 is well suited. Also, during long-term storage, it is recommended to keep the stop screw fully tightened.