Info > Technical Tip: Restraining Devices

Thrust forces in buried water mains are created when the pipeline changes direction (at bends and tees), stops (valves, hydrants and dead ends), or changes in size (at reducers). In order to keep the pipeline intact, the traditional methods of restraint have been the use of thrust blocks, clamps and tie rods, and mechanical joint retainer (locking) glands.

Thrust blocks are usually made of concrete; however hardwood and stone are occasionally used.

Technical tips are for informational purposes only.

Rods are used in many ways, either by themselves or with other methods, to restrain thrust forces. The number and size of rods are limited to economics and practicality. All steel materials should be coated with bituminous paint to retard deterioration.

One of the most popular field methods of joint restraint is the use of Ebba Iron’s MEGALUG® mechanical joint restraints. MEGALUG®’s install using an ordinary wrench (box, ratchet, or air-driven), because the torque-limiting, twist-off nuts automatically shear during tightening when the proper torque is reached. MEGALUG®’s have a working pressure rating of 350 psi for 3-16 inch and 250 psi for 18-48 inch. Ratings are for water pressure and include a minimum safety factor of 2 to 1 in all sizes.

For hydrant run outs, MJ tees have been developed with restrained rotating glands on the branch. Hydrant tees (also called swivel or anchor tees) are available in the following sizes: 6” x 6”, 8” x 6”, 10” x 6”, 12” x 6”, and 16” x 6”.

U.S. Pipe’s FIELD LOK® gasket system is a truly unique means of providing instant joint restraint for 4” through 12” Ductile Iron TYTON JOINT® pipe and fittings. By simply inserting a FIELD LOK® gasket into the socket, joint restraint is provided. No pipe surface preparation is required. Stainless steel locking segments molded into the FIELD LOK® gasket grip the pipe to prevent joint separation. FIELD LOK® gaskets are suitable for maximum working pressures of 250 psi.

U.S. Pipe’s TR FLEX® Restrained Joint System (pipe and fittings from 4” through 64”) is a completely boltless joint using the time proven TYTON JOINT® seal. The joint is suitable for 350 psi working pressure for pipe and fittings sized 4” through 24” and 250 psi working pressure for sizes 34” through 54”. Ductile iron locking segments, inserted through a slot(s) in the bell face, provide a positive axial lock between the bell interior surface and a retainer weldment on the spigot end of the pipe.

One word of caution: the restraining devices discussed above, except for thrust blocks and tie rods, make the joint a rigid connection after assembly. If deflection of the joint is required, it must be done prior to completed assembly and no future deflection is possible.

As a final reminder, the problems involved with any method of thrust restraint are important to understand for each of us involved in the water works industry. With new products being developed all the time, it is recommended that you contact your Water Works Supply Corp. representative for information on the best device for your particular situation.

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