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When Should You Use No-Hub Fitting Restraints?


No-hub piping transformed the design of drainage pipes, which for years, had required pieces to be connected by melted lead in a procedure that was expensive and difficult to execute well. Shielded no-hub coupling emerged as a safer and easier solution. Most importantly, it worked well and didn’t wear out.

Since then, No-Hub couplings have proven themselves to be immense time-savers for connecting cast iron and plastic piping. They do pose one major problem, however, and that is their incompatibility with most fitting restraints.

Why Are Fitting Restraints Important?

Fitting restraints serve to keep the pipe and to fit together under thrust conditions. If restraints aren’t present in a no-hub system, and if thrust forces increase to more than 10 feet per head, the pipe is at high risk of separating from the fitting.

If that happens, it can cause expensive property damage and tarnish the reputation of the contractor.

What Causes Pipe and Fitting Separation?

Thrust forces increase for several reasons. The two most common are:

  • Lack of overflow point, which can cause multi-story backup and high pressure in the case of a blockage, and
  • Hydraulic jump, or the backup of fast-moving water when it encounters a slower flow.

A hydraulic jump happens when water flowing quickly down a vertical pipe at high speed runs into water flowing more slowly through a horizontal pipe.

What Are the Consequences of a Pipe and Fitting Separation?

Pipe and fitting separations aren’t just a “what if” scenario – it’s happened, and it’s been devastating.

When the Indianapolis Colts’ Lucas Stadium was scheduled for unveiling in 2008, the deadline mandated that the plumbers expedite their work. Fitting restraints were left off of the rainwater system. When a storm came, the pipes separated from the fittings, and the flood destroyed the costly IT systems that had just been installed in the basement.

A similar issue happened at the University of Pennsylvania Health System Translational Research Center in 2012, not long after the building was completed. The owner had already moved in when an intense rainstorm hit the region. The volume of rainfall caused pressure to build in the piping systems, and an unrestrained rainwater leader failed, crashing through a stairway ceiling and causing a massive flood.

If the water in the vertical pipe is moving fast enough and if the full flow goes on for long enough, it can back up the vertical pipe and cause enough pressure to make the pipe and fitting separate.

These situations led to millions of dollars in damages – $15 million at Lucas Stadium, which experienced two additional pipe failures after 2008. But these are just two of the best-known examples of what can happen if a no-hub system fails.

What Can Be Done to Protect No-Hub Fittings?

The standards issued by the Cast Iron Soil Pipe Institute (CISPI) prescribe movement restraints for all pipes 5 inches in diameter and more extensive. These restraints need to be in place at all piping joints, and anywhere the system changes direction. This is an expensive proposition for many contractors who work with no-hub systems.

It’s easy for some designers to ignore this guideline, mainly if they aren’t familiar with restraint regulations added to the International Plumbing Code in 2009. According to Chapter 3 of that code, “Piping in a plumbing system should be installed to prevent strains and stresses that exceed the structural strength of the pipe.” This provision mandates the use of fitting restraints even in hub-free piping systems.

Unfortunately, traditional pipe fitting restraints aren’t compatible with no-hub systems. You need to implement an alternative solution, and that solution needs to be laboratory tested and certified by a third-party engineer.

Why Can’t You Use Field-Devised Methods?


Developing a solution on the job site can be necessary in some cases when there’s no other choice, but it’s a dangerous proposition when restraints are involved.

Field-devised restraint solutions often involve the use of tools that aren’t stable enough for a fitting restraint. For example, some contractors might be tempted to use riser clamps to create an ad hoc fitting restraint. These tools are not tested for effectiveness in thrust conditions.

A field-devised restraint system also carries the risk of becoming temporary, fitted in time for testing, but removed when it starts to get in the way. Considering that these substitute restraints are usually more time-intensive to create and often more expensive, there is a great deal of risk involved should they fail or be removed.

What Are the Benefits of a Tested and Certified Solution?

An established no-hub fitting restraint, one which has been developed by experts and has been proven effective, saves money and time for the contractor and the property owner. The HoldRite #117 Series restraint is an ideal example. It offers:

  • Protection against water blowouts in high-thrust situations
  • Prevention of joint separation due to misalignment or lateral movement
  • Simple installation, no on-site adjustments or special tools necessary
  • Compliance with all relevant plumbing codes
  • Alignment with pipe manufacturers’ installation recommendations and the CISPI Handbook.
  • Construction of highly durable stainless steel galvanized metal, and/or black iron

HoldRite’s #117 series features direction-change and joint restraints for pipes of all standard sizes. Each has undergone thorough testing and has been verified effective by objective third-party engineers.

Tell Us How We Can Help

HoldRite offers the #117 series through wholesalers nationwide. We’re also available to answer questions about our products directly. 

If you are an engineer, contractor, or wholesaler, call us to ask about our No-Charge VIP Estimating Service, which can help you to see the savings involved in using our no-hub fitting restraints and potentially uncover other savings opportunities.

The more you save without sacrificing quality, the more value you deliver for the client. Find out how you can deliver results that are safer, more cost-effective, and likely to get you recommended for the next job.