Refrigerant Evacuation: HVAC Vacuum Hoses and Fittings

by Aug 25, 2022

Vacuum hoses and fittings are a handy piece of equipment for vacuum pumps responsible for suctioning under negative pressure.

In the biological sciences, vacuum pumps for filtering, solvent distillation and concentration, solid phase extraction, freeze drying, and other processes. Despite having a similar purpose, selecting a new vacuum pump requires considering several factors. Let's learn all about HVAC vacuum hoses and fittings in this article.

Vacuum is an important component of several composites technologies. There aren't any other effective techniques to exert tremendous pressure on huge irregularly shaped regions! This article discusses the hoses, fittings, and connectors between your vacuum pump and your component.

There are various needs for different procedures. Although you might not require much total vacuum for bagged wet-layup, you still need to be able to control it because of all the resin that needs to stay put. Vacuum is the key to infusion, and in many instances, the more vacuum, the better. Pregnant women add a lot of heat and maybe a lot of extra pressure to an autoclave. Your vacuum equipment must correspond to your procedure.

VACUUM HOSES

The six most frequent hose types seen in composites shops have a smaller diameter than you typically require for individual pieces. Small hoses are okay because, aside from when first bringing down a vacuum bag, you (ideally!) don't need a lot of flow for most processes.

The least expensive material is a plastic (polythene in this case; ordinary infusion hose) that is both rigid and manageable. It won't withstand pre-preg heat, but it'll be okay up to about 140F/60C and suitable for post-curing. You can use it in a disposable manner, but it can also be made more durable by adding barbed or push-to-connect connections.

Please avoid using the clearer, more flexible PVC hose, as it chokes off when bent over tight corners and is easy to crush. It's frequently used for infusion. However, it is a bad option—at least for the vacuum side. All of the skilled "infusers" I have ever worked with or observed utilise silicone or (sometimes) polyethylene hose.

The black hose in the "air-hose" type with a rubber coating is a more durable option. This hose is extremely durable and works well at room temperature. A pre-made 300 psi air hose with vacuum fittings rather than air fittings is the black hose in this picture. The ideal hoses to use are those rated for higher pressure since you need a wire-reinforced hose, and these can typically withstand moderate heat up to 180°F (80°C) or so.

Air or vacuum hoses can be made anywhere that makes hydraulic hoses to order, and they may be far less expensive than McMaster-Carr or your local equivalent! You can either purchase hoses or adding fittings. You can also have them customised to your needs by a local hose shop.

The air hose won't do for your pre-pregnancy cooking endeavors because heat adds another layer of intricacy. Radiator hoses or coolant hoses made of silicone are common for ovens. You can construct it using hose clamps, barbed fittings, and a silicone cover reinforced with a wire. If you wish to build your hose, you can buy it already cut to length or have a hose shop make hoses to your specifications. These are typically rated to withstand temperatures in the 150C to 300C range, which is enough for most non-aerospace pre-preg operations.

The tan hose in the image is an oven hose for use up to 450F/230C and is called the Airtech Airflow 65R. This hose features a silicone rubber coating over a metal core, making it somewhat flexible and convenient to use with vacuum bags when placed on top of food to be cooked. You can also use it with low-pressure autoclaves.

The green hose is a vacuum with an autoclave rating that can withstand high temperatures and external pressure up to 150 psi/10 bar. It's the lower end of autoclave hoses. More expensive metal can withstand pressure up to 1000 psi and temperatures up to 1000 F/500 C. Low-end "cook hoses" cost around $10–$12 per foot, roughly twice as much as good quality room temperature hoses. They will last very long if you don't goop them up with resin, which is harder to accomplish with pre-pregs.

One more thing about colour and service type: Try to color-code the hoses if you run a facility where many people use them to help avoid mistakes. It's crucial if you cure products in an oven or autoclave because errors could have serious consequences!

Big Hoses

We will try to dissuade you from using pipes larger than 1/2′′ / 12mm internal diameter unless you construct extremely large items. They are required in many situations, so if you're using them, you're already doing it correctly. I believe that the two best options are a larger factory-wide vacuum system or several cells- or station-specific vacuum pumps.

A big vacuum system has the drawback of being vulnerable to issues in one region affecting other parts. Backup pumps are certainly an option and may be quite helpful from a servicing standpoint. However, since the vacuum is essential to many composites processes, letting your vacuum level drop while someone else works elsewhere can be detrimental. If you decide to use a hard-plumbed vacuum system, try to utilize a few accumulators scattered around your facility to absorb vacuum drops and even out the system. Large diameters of heavy gauge PVC can be used, with vacuum plumbing serving as the accumulator.

Small pumps close to various work areas are beneficial because they may be adjusted and give the system local control. The hose plan with tiny local pumps will rely more on connectors and small hoses and less on large hoses.

If big diameter hoses are necessary to manage vacuum distribution, you can utilise them to install manifolds in locations where smaller hoses can attach to components. A hydraulic hose or a large air hose reinforced with wire works well. For this, a clear PVC hose with wire reinforcement works well and is cheaply priced. To go with, you'll need large fittings.

CONNECTORS

You'll need a way to connect all lovely hoses to your pump and bag in addition to each other. Hard piped hoses are acceptable for stationery items and unlikely to get gummed up, but removable hoses are usually preferable!

First, a brief explanation of connector kinds only three of the five possibilities shown in the figure are truly suitable for vacuum work at the composite level.

Regular air hose fittings are on the left; while they can function, they are designed for pressure rather than vacuum, which means they can leak and cause all kinds of problems. Some of them will perform well for a while and are inexpensive. You might find air pressure quick disconnects that function okay because there are wide varieties. It will mostly be alright for a low-vacuum wet layup operation. There’ll be a lot of wet resin around and the possibility of going up fittings.

They come in three different materials: steel, brass, and stainless steel; brass and steel (on the transparent hose and plate fitting) cost roughly half as much as stainless steel. Because brass is inexpensive and less likely to rust when in touch with moisture, I prefer it.

The most important thing is to select something dependable, affordable, and adequate for what you're doing. There are other, more expensive varieties of fast connect fittings used for vacuum, and I have used them while working in other businesses, and they are fantastic.

For usage with the plastic hoses, two tiny push-to-connect connectors in the centre are silver in colour. These can be useful for low-cost connectors for wet-bagged and infusion activities at room temperature.

The cone-shaped object on the right illustrates a high-vacuum fitting that uses a pair of flanges and a compressed sealing ring. This kind of fitting is frequently seen on high-vacuum pumps, and I used one of them to connect to a Leybold pump I once owned. The benchmark for a vacuum can be seen in the very high vacuum systems utilized in the lab, scientific, and upscale industrial activities. They are overkilled for composite work. However, you might need to use them to communicate with pumps and filters, so it's a good idea to be aware of them.

Cam-lock-style connectors are an excellent option for bigger hoses. When you buy ones rated for it, they are safe and handle vacuum quite well.

Sealing Threads

Pipe threads are made to get closer as you screw them in, but to achieve complete vacuum-tightness, they also require some thread sealant. Both liquid thread-sealant and PTFE tape function properly. Since they are softer and far less likely to corrode, brass fittings are good because they are also affordable.

Vacuum bag sealant tape is frequently wrapped around the threaded connections of fittings. When trying to find leaks without knowing where they are, this is done primarily as a precaution or to seal the low-hanging fruit first. My fittings are often like this. Leaking shouldn't be an issue if you use thread sealant correctly and tighten your threaded connections thoroughly.

BAG PENETRATIONS

You'll require a method to pass that vacuum through the bag. How to accomplish it and commonly used fittings are covered in this section. It's not the case with vacuum infusions. It only applies to bagged wet layup and pregnancies. These lovely through-bag fittings shouldn't be used for infusion because you'll destroy them.

Check out the section of tube bag assembled amid infusion mesh and a fitting for another approach to safeguard your vacuum connectors. It's an excellent solution when there isn't space for a fitting under your bag. Then, insert the vacuum fitting into a second 4" tube bag filled with strips of infusion flow media. Similar to a remote vacuum port, it. A few spots of bag sealant tape are used to hold the infusion mesh together and prevent it from separating. One end has the vacuum port, while the other is sealed with additional sticky tape to fit beneath the perimeter bag seal.

On the upper right, another style of through-bag connector passes through the sealant tape on the bag's edge. The bag is placed over it on another strip of sealing tape, which lays on top of it. The breather covers the part with the opening on the bottom face.

Finally, their most basic vacuum connection is the large, wavy man to the right, which consists of a hose fitting for a rapid connection on one end and something wrapped around the end. It's merely a piece of polyethylene vacuum infusion tubing with infusion mesh, a barbed fitting, and a fitting. Breathable clothing also works well. Avoid just jamming a hose beneath the bag without a dispersion medium over the end since doing so will cause the load to burst or the hose to fill with resin and obstruct the flow. If you're bold, you can bypass connectors and hoses by plumbing a barbed connector to your vacuum pump. Just be careful not to suck resin into the pump. Otherwise, it won't work as a vacuum pump anymore.

A vacuum regulator is a final item to consider here. It's the brass object with a knob attached to the back hose. You can lower your vacuum level with a regulator. It's helpful when you wish to prevent resin bleed during bagged wet-layup or, in some circumstances, during infusion. You'll need an in-line gauge to check your vacuum level as you turn the dial.

GAUGES

You need to know how much air is missing from your bag or how much vacuum you have. A gauge is crucial in this.

An analogue gauge is a fantastic place to start because it's affordable and gives you a good indication of what's happening. Opt for one with an oil-filled dial that is large enough to read. Almost everything you want to do as a pastime should be good with this. To acquire a quick browse on the vacuum pressure without touching buttons, they are also useful for hard piping onto manifolds, pumps, and catch-pots.

Digital versions provide a more precise reading of your vacuum level and, more significantly, variations in your vacuum level. A digital gauge, especially an absolute gauge, will help you better understand what's happening if you find yourself performing pre-pregnancy procedures or infusions on a commercial level.