I have a garden water system which runs via a auto timing system, but having problems with leaking at the T joins, and where the poly pipes are attached to timers.

I have tried using metal screw type tighteners, the plastic ones that are recommended, but still the leaks continue.

Have re cut the poly pipes, replaced the tighteners, reduce the water flow, put in a Flow restrictor, so now at wits end. Help would be appreciated, have even thought of using Marine silicon [glue] before placing the tighteners on, would this help?

Post a picture. Something tells me you need a flexible connection someplace.

Did you deburr the edges and make sure the pipes were squeaky clean when inserting them into the fittings.

No I have not de-burred, or washed the poly pipe or the T piece, will do that tomorrow. If that does not help will send a photo, thanks for the suggestion.

PK.. https://www.askmehelpdesk.com/images/icons/icon14.gif
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The new fitting should not have to be cleaned, but deburring and cleaning the pipe is dependent on what method was used to cut it. If it was cut with a hacksaw, the enge should be deburred, cut flat and perpendicular to the pipe and all loose debris should be removed.

In most fittings, the edge assures a uniform force on the seal. If it's cut at any angle, then there is a tangential force on the fitting and it could leak.

If it was cut with a racheting pipe cutter, the edge will be nice and clean. Product Listing - PVC-Pipe-Cutters

If the fitting os "O" ring based, you might remove the ring and place a little "silicone grease" in the hardware store in the plumbing section on the "O" ring before re-assembly.

KBC:

PVC (Poly Vinyl Cloride) glue on polyethelyne? I don't think so. The tubing is also not buried below the frost line, so it has to be able to move. It also has to come up every once and a while to reach the sprinkler heads.