Push-in fittings and their use under the microscope
Praise to the person who invented push-in fitting systems. They brought about a revolution in the efficient distribution of air and other media to the applications themselves. In this respect we have probably reached the maximum possible convenience of connecting and disconnecting. But are all push-in systems the same? Let us take a closer look at this way of connecting.
What options does the range of push-in systems offer? Actually fairly similar ones to other systems for connecting and distributing air or other media. And we can quite happily start with the medium, because what matters is what the surface of the fittings and tubing comes into contact with and what interaction this causes. With all components, therefore, pay attention to whether they are suitable for chemicals – aggressive media – or, conversely, approved for contact with food. We always state these parameters together with the description of the applications the particular fitting or tube is suited to. These are mainly automation, measurement and control technology, or pneumatic compressed air lines in industry, mechanical engineering and automotive technology. Those are the most common areas where push-in systems are used on production lines.
General classification of push-in fittings according to use:
- standard fittings for ordinary applications
- fittings adapted for higher pressures
- chemical-resistant fittings
- fittings suitable for contact with food
- antistatic version
- fire-resistant fittings according to DIN 5510-2
- fittings resistant to sparks from welding equipment
And what are the disadvantages of push-in systems, actually, when we see how wide a range of uses they can cover and how broad a choice we have? Everything begins precisely with the correct choice according to the required parameters, which eliminates most of the shortcomings. One of the very few disadvantages that remains after a suitable choice is the generally poorer resistance to mechanical stress. Part of this is solved by the rotary version of the fittings or by specially manufactured polymers the tubing is made from. And as for the rotary version – thanks to ball bearings these special fittings handle rotation of up to 1500 revolutions per minute. And as for the disadvantage that part of the fitting range has, it is the impossibility of use with vacuum. Why? We will break that down in the following part, where we look at what the inside of such fittings actually looks like.
Taking a push-in fitting apart
The main part of a push-in fitting is the body itself (the corpus) – made of plastic or of certain metallic and stainless materials, which on at least one side conceals rather sharp “teeth” of stainless steel behind a release ring (elsewhere referred to as a retaining ring). This always has to be pressed towards the fitting in order to open the teeth and either insert or withdraw the tube. This perfectly functional and simple system is in most cases complemented by an O-ring hidden inside the fitting (usually NBR), against whose wall we “push” the tube for maximum tightness, and then we release the ring – the joint is complete. It could only come apart under vacuum.
Other systems, especially for larger diameters, use rotary locks as the retaining element. We can come across this version in various air distribution lines in halls and plants.
And what is the opposite end of a push-in fitting like? There are many options – from threaded fittings and identical push-in fittings to adapters, barbed stems, throttle valves or shut-off valves, right up to large manifold fittings.
And what about the tubing?
Push-in fittings are intended for elastic pneumatic hoses with a calibrated outside diameter. This diameter commonly starts at 4 mm and in most cases ends at 12 or 16 mm. The most common material used for manufacture is polyurethane – a polymer produced by the polyaddition of diisocyanates and di- or polyhydric alcohols, forming a carbamate bond. The advantage of such tubing is high flexibility, but also resistance to mechanical stress. Other commonly used materials are polyamide or tubing made of the branded Kynar HD4000 granulate for the most aggressive media. On the other hand there is silicone – in most cases transparent, for use in the food industry. Such tubing must of course be entirely harmless, and therefore it complies with the FDA and 1935/2004 EC directives.
You can explore our entire range of hoses here: Hoses for compressed air
What is there to add in conclusion?
The push-in system is the best friend in the field of connecting tubing and distributing the medium to the application. You do not have to train the staff at length before installation, you do not have to invest dizzying sums in acquiring the components, let alone in tools. It is enough to always keep to a few basic rules and to choose well according to the parameters – then the whole system will serve you for years without worries.
You will find the most popular plastic push-in fittings in our online shop here: Push-in fittings
And all the connecting material here: Connecting material for compressed air