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Hydrostatic Testing Explained


Hydrostatic testing, in essence, is a way in which pipelines, plumbing, gas cylinders, boilers, and fuel tanks can be tested for strength and leaks.  It basically involves filling the pipe with a liquid that may or may not be dyed to aid in leak detection, and pressurization of the pipe to a specific test pressure.

Hydrostatic Testing

Hydrostatic testing is the oldest form of testing plumbing drain systems and is the most common below grade test method as it doesn’t require a lot of special equipment. Hydrostatic testing consists of testing of the drain system using the pressure of a column of water referred to as a “head” of water.

  1. Remove the drain system clean out cover.
  2. Insert a test plug to the city side of the cleanout.
  3. Fill the drain with water to the height of the cleanout.
  4. Allow the water to stand for a period of time, approximately 30 minutes or more.

In some situations, a cleanout may not exist or cannot be located. In these cases, a new one may need to be installed. Alternatively, if possible, testing from a toilet location can be done.  This will usually consist of removing the toilet from the floor and using the open drain beneath it.

In either of these instances, if the water level drops over the period of time allotted, there is a leak in the drain system.  If a leak is detected, a camera may then be used to determine where a leak may be likely to exist, and to assess the overall condition of the pipe in order to evaluate the value as far as repair versus replacement.

Hydrostatic testing is considered one of the most accurate ways of locating leaks, because it will find even the very smallest leaks, depending upon how long you run the test and how long the water is allowed to stand.

The plumber may also perform an isolation test to determine the specific drain line area or branch where the leak exists.

Isolation Testing

Isolation testing is an extension of hydrostatic testing and is typically performed after a system has failed a system wide hydrostatic test to find the location or area of a leak.  Isolation testing blocks the branches of the plumbing system in sequence, and it tests each branch for leaks individually through hydrostatic testing until the specific branch or area that is leaking is found.  This is usually done by inserting a test plug down the drain to allow testing at specific areas.  A camera is often used to assist in locating branches and positioning of test plugs. 

Isolation testing increases the cost of testing, and in old systems where the entire system is near or at its life expectancy, it may not be the most cost efficient option, since replacement of the entire system would typically be needed eventually anyways.

This article has been shared by Direct Service, Construction and Design to specifically accommodate our intended clientele.  The intent of sharing this information is to better inform the public of these general topics, expand knowledge and safety for all and provide crucial information in regard to their MEP and building systems and/or assets. It is NOT our recommendation that any article recommendations or how-to scenarios be attempted by anyone other than a qualified or competent person.