The Right Fitting for the Application: A Guide to John Guest Push-Connect Fittings Materials

Push-connect fittings have revolutionized plumbing and fluid transfer systems, offering ease of installation and reliability. The most trusted brand in this realm is John Guest, renowned for their quality and innovation. In addition to their history, experience, and quality, what sets John Guest apart is its array of materials for push-connect fittings, each catering to distinct needs and environments. Let's delve into the differences between these materials and their applications.

Grey Acetal Copolymer:

The PI Range (John Guest part #s starting in “PI”) of inch-size push-fit fittings accommodates tube sizes ranging from 5/32" OD to 1/2" OD. Constructed from gray acetal copolymer and featuring a food-grade nitrile O-ring, these fittings are specifically designed for applications involving foodstuffs and potable liquids. Additionally, they are compatible with air and inert gases, making them versatile for use in CO2 lines, pneumatic applications, and vacuum systems.

The differentiating features are:

• Nitrile O-Ring: The nitrile O-ring holds up well when exposed to oil, which makes it effective for use in compressed air lines where oil from the compressor tends to seep into the lines.
• Higher Pressure Ratings: The grey acetal fittings are rated at a maximum pressure of 230 psi at 68˚F for sizes 5/32"-5/16" (typically 1/4” for the imperial / inch-sized fittings) and 150 psi at 68°F for sizes 3/8"-1/2". This is a higher max pressure rating than the Polypropylene fittings, making them suitable for higher pressure applications.

Polypropylene:

The PP Range (John Guest part #s starting in “PP”) of inch-size push-fit fittings accommodates tube sizes ranging from 1/4" OD to 1/2" OD. Constructed from white or black polypropylene and featuring a food-grade EPDM O-ring, these fittings were specifically developed for filtered pure water applications. John Guest Part #s will start in “PP” and end with “W” for white polypropylene or “E” for black polypropylene.

The differentiating features are:

• EPDM O-Ring: The EPDM O-ring has an improved chemical resistance from the nitrile O-ring, particularly for under-sink cleaning supplies. We have seen the nitrile O-rings in acetal fittings be degraded by under-sink chemicals, causing issues, so we always recommend the polypropylene fittings for that purpose. However, the EPDM O-rings do NOT hold up well to oil, so we do not recommend polypropylene fittings for compressed air applications.
• Slightly Lower Pressure Ratings: The polypropylene fittings are rated at a maximum pressure of 150 psi at 70°F – slightly lower than the acetal fittings, but more than sufficient for household installations.
• White vs. Black: Using white polypropylene vs black polypropylene is mostly a matter of personal preference, but the black color tends to hold up better in UV-exposed environments (in the sun). We sell significant volume of black polypropylene into the Agriculture market for that reason.
• Price: All things equal, the polypropylene fittings are slightly less expensive than the grey acetal fittings.

This all refers to imperial / inch-sized push connect or push-in fittings. We also offer metric-sized John Guest fittings in both grey acetal and polypropylene. There are color differences in the metric-sized fittings that are different from the inch-sized – to be covered in a later blog!

Specialty Sales has been a John Guest distributor since they originally brought their innovative push-connect fittings to the US market, and we continue to be one of the largest John Guest distributors in the country. Let our sales team know if we can be helpful in finding the right fitting for you.