What is Water hammer? Water hammer in a steam system occurs when water inside of a pipe or vessel is accelerated and forcibly impacts a piping elbow, transition, or downstream piece of equipment. This results in a knocking sound similar to hitting the pipe or vessel with a hammer, hence the name water hammer. The issue is that these slugs of water can be accelerated to very high speeds and the impacts that cause these hammer sounds can contain a lot of force. This can damage equipment or cause piping to fail, which is dangerous to any operators in that area. 

Any steam that condenses in a steam line will be drawn to the low points in the piping by gravity. If the line is not drained properly, that condensed steam will start to gather. This will happen until the piping fills to a point where the line velocities pick up that slug of condensed steam accelerating it to a high velocity. It’s not uncommon to have a steam line with an internal velocity of 100 -150 ft/sec. As the liquid slug is accelerated to the line velocity that slug delivers a large force to whatever piping elbow or piece of equipment is downstream. In an ejector this water hammer effect can cause damage to the ejectors motive steam nozzle. While wet motive steam is not good over long term operation, a line filled with a solid slug of water is capable of shearing off the ejector’s motive nozzle, which would prevent the ejector from working correctly and require the ejector to be removed from service for repairs.

In order to help prevent this, steam lines should be slowly heated up prior to start up. This can be done by opening a bleeder and allowing steam to flow through the previously dormant piping. This allows that pipe to heat up before the full steam flow is placed into the line. If the full steam flow is placed on a cold line the amount of condensate generated can overwhelm the condensate drains and cause water hammer. Rapidly heating up the piping can also put a lot of unnecessary thermal stress on the piping. The steam lines to an ejector system also need to be properly piped and drained. The steam piping should be piped in a way that allows condensate to drain out of the piping and not gather at low points. If the piping does have a low point or a riser then a condensate trap should be placed in the steam line to drain any gathering condensate. It’s also important that the operation of steam traps are verified before start-up and it’s confirmed that all drain trap isolation valves are open.

Cooling water lines going to a vacuum system’s condensers need to be vented at the high points at start up. As the cooling water lines are slowly filled, the high point vents on a system should be opened. This allows air that is trapped to escape and ensures that the lines are completely full of water. If the lines are not vented properly it can cause air lock or change how the water is distributed to the various condensers in a system. In severe cases, the top tubes of the condenser can run dry, causing a loss of performance and possible tube damage.  

Air lock occurs when a pocket of air in a line prevents or restricts the water from flowing freely. This is more likely to occur in a line operating at a lower pressure where there is not enough force to push out the pockets of air. Since condensers tend to be installed at elevation the cooling water lines often operate at very low positive pressure or even sometimes under vacuum. This makes them a prime target for cooling water flow issues generated from air lock. Ensuring that all the high points in your cooling water lines have vent connections and making sure these points are vented when the pipes are being filled helps to ensure that air lock does not cause a performance problem.