Quick-Connect and Simple Compression Fittings for Water Filtration Equipment

Water News in a Nutshell.


In a Nutshell;  Water treatment devices like undersink filters and reverse osmosis units need fittings to connect tubes to tubes and tubes to fixed objects like filter vessels.  The predominant styles are quick-connect fittings and plastic compression fittings.  This article is an introduction to the two styles. 

Top to bottom: 1/4″ John Guest, Mur-Lok, and Jaco tube tees.

 The most commonly used fittings on reverse osmosis units and undersink water filters are the nylon compression fittings called Jaco and the more recently developed push-in quick connects called John Guest. There are many manufacturers of both styles, but the imitators are most often referred to by the name of the originator — the way that all soft drinks are sometimes called “cokes.” The fittings shown here (and featured in our products)  are from the original manufacturers — John Guest and Jaco — and we also supply the superb double-o-ring Mur-lok Fittings from the G. A. Murdock Company.

The two fittings styles can be interchanged without a problem. If your undersink unit uses Jaco fittings and you want to replace one or more fittings with a John Guest style, there’s no problem. There is, however, one essential rule you must follow: Jaco fittings must always be used with a tube insert, and tube inserts are never used with John Guest or Mur-lok

Tube inserts must always be used with Jaco-style compression fittings to prevent leaks.

quick connects.

To connect Jaco Fittings, back the nut onto the tube, insert the tube insert as far as it will go into the threaded body of the fitting, then screw on the nut. Tighten it as tight as you can get it with your hand, then take one more complete turn with a wrench. No more than one. Over tightening will eventually result in a leak.

With John Guest style, be sure that the tube is cut squarely, then push it into the fitting until you feel it hit bottom. It’s done. If you need to remove the tube, be sure that all pressure is off the fitting, push in on the collet with your thumbnail, and pull the tube out. Remember that you don’t use a tube support with quick connect fittings.

Tubing used for filters and reverse osmosis units is always measured by its outside diameter. Undersink reverse osmosis units use 1/4″ OD tubing, and some units use a mixture of 1/4″ and 3/8″ tubing.

Fittings of both types are available for larger tube sizes, but this article applies only to tube sizes up to 3/8″ OD.


Above is a clear plastic model of a Mur-lok quick connect fitting. The white insert is called the collet. Note that it has two o-rings. Most quick connects have only one.

Reference Source:  Pure Water Products

More pages to visit:

John Guest Fittings

Parts for Quick Connect Fittings and How to Fix Them

The Most Common Fitting Sizes for Filters and Undersink RO Units

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