Most applications involving vacuum pick-and-place components use small-diameter hose and tubing—the same hose and tubing utilized on similar-sized pneumatic installations involving the connection of valves and actuators, for instance. The most popular type of tubing used in both of these applications is polyurethane, which is more commonly known as “PU tubing.”

Polyurethane tubing is appropriate for small-diameter applications of less than 5/16″ (Ø8 mm) internal diameter (ID). Anything larger than this and there is a risk of tubing breakdown. Don’t forget that most tubing is valued at an operating or burst pressure, not vacuum. Above 8 mm ID, different tubing should be utilized. A prevalent type would be a wire-reinforced PVC hose.

This kind of hose is rated up to 29.9″Hg with internal diameters of about 2″(50mm). That definitely covers most vacuum applications. If larger diameters are needed to prevent vacuum loss over long distances or for very high flow applications, rigid pipe such as PVC, ABS, or steel would be needed.

The bend radius of wire-reinforced PVC is also perfect, bearing in mind the diameter. For instance, a 2″ ID hose would have a bend radius of about 5″ (125mm). This might be hard to “thread” through a robot arm, which is why in a lot of cases, this vacuum hose that could be attached to a large end-of-arm vacuum tool would be attached to the outside of the robot arm. Not the prettiest, but effective.

In fact, robotic integrators sometimes select compressed air venturi systems over vacuum pumps for large vacuum tools purely because of this fact. It’s easier to thread compressed air PU tubing through a robot arm than to employ a floor-mounted pump that delivers vacuum through a large-diameter hose. Of course, if the tool is one of many that is attached and detached repeatedly through an automatic tool changer, then the integrator has little choice in the matter as there is no auto tool changer that accommodates large-diameter vacuum hose.

So, there are a couple of basic choices for vacuum tubing or hose: PU and PVC reinforced with wire. I stress that wire-reinforced PVC is NOT the same as braided PVC hose, as shown in Fig. 5. This will collapse at virtually any vacuum level—a common initial mistake made in choosing a larger-diameter vacuum hose.

So that’s the tubing taken care of, but how do you connect this tubing to vacuum components like cup fittings, valves, and so on? Of course, nowadays, the most common fitting choice for PU tubing would be a push-to-connect (PTC) or push-in fitting. However, with PTC fittings, ensure they are suitable for vacuum use. The original designs of PTC fittings are sealed better under pressure, which is a vacuum installation that doesn’t exist. The PTC fitting utilized should also be tested for leakage under sideload. Good PTC fittings won’t present a problem but ensure that side load-sealing capability is present. The real world provides the real test, after all.

The more traditional fittings, like “rapid”-type fittings originating from Europe and compression fittings, can be utilized. However, these are very difficult in installation, and although, if installed correctly, guarantee a leak-tight seal, the PTC fitting option is certainly faster and less costly. The compression fittings are very much a one-time connection. Once the ferrule is compressed around the OD (outside diameter) of the hose, it’s permanent. If the fitting is utilized again, this part of the tubing, including the ferrule, should be discarded.

For larger-diameter hose, the PVC-type described previously is not fit for PTC fittings. Traditional fittings, like the hose barb and “worm drive” clip, are the most popular and certainly most readily available. Of course, there are more fancy and elaborate fittings for larger hose, but as the hose is usually a permanent installation, the hose barb and clip are more than adequate.

Tubing choice is normally determined by what is available onsite at the time of installation. Polyurethane tubing is the most common because it is normally used in the corresponding pneumatic circuits. For larger hose, this is usually not in stock at the end-user or machine builder. When choosing a vacuum hose, do not search the Internet for simply “vacuum hose.” You will be digging through vacuum cleaner hose suppliers for a lot of time. Attempt “reinforced vacuum hose” instead. That should bring up a good list of potential suppliers of the suitable wire-reinforced PVC mentioned earlier.

References and Resources

• Polyurethane Tubing