And how do they work?
DC Pipe Interrupters seem like a very appealing solution for Fluid Category 5 applications, as they are much cheaper and easier to install than alternatives such as a Break Tank & Booster Set. Often, we receive phone calls from customers who have seen the DC Pipe Interrupter online in the Category 5 section of a website, and want to use it for their industrial application, saving themselves thousands of pounds. Unfortunately they are frequently left disappointed, as the DC Pipe Interrupter is only suitable for a handful of applications – let’s investigate why…
The definition of “backflow” (taken from the Water Regulations Guide) is a “flow upstream, that is in a direction contrary to the intended normal direction of flow, within or from a water fitting”. Put simply, once a Water Company supply you with potable water, they don’t want it back in their distribution pipe.
There are two different types of backflow: “back siphonage” and “back pressure”.
“Back siphonage” is when you have a vacuum on the supply to an outlet, causing water to siphon backwards, potentially causing contamination. “Back pressure” is when the downstream pressure is higher than the supply, forcing water to flow backwards.
Some backflow prevention devices are suitable for both “back siphonage” and “back pressure” applications. Others, such as the DC Pipe Interrupter, are suitable for “back siphonage” only.
DC Pipe Interrupters are designed to have a permanent atmospheric vent – you can clearly see the vent holes on the side of the valve body. If a “back siphonage” situation was to occur, the water would discharge through the vent holes rather than flow backwards, potentially causing contamination. Any restriction downstream of the Pipe Interrupter, such as an isolating valve or trigger operated wash-down gun, will cause water to leak via the vent holes. Therefore, the DC Pipe Interrupter is only suitable for open outlet applications.
In addition to only being suitable for “back siphonage” applications with an open outlet, there are further limitations to consider when using the Pipe Interrupter. They can only supply a relatively low flow rate (12 litres per minute) and must be installed vertically, to allow water to flow though them without dispensing out of the vent holes. Also, they are only capable of supplying low pressure, which is generated by the height of the Pipe Interrupter above the water fitting it is supplying.
Essentially, there are only a few applications that they are suitable for!
Arrow Valves offer four different models of DC Pipe Interrupter which are each designed for a specific application:
Model DC15C257 is for use with mains fed urinals, as an alternative to a traditional cistern. The DC Pipe Interrupter has 15 mm compression connections must be mounted a minimum of 150 mm above the sparge outlet.
Model DC20F257 is designed to screw directly on to a Hose Union Bib Tap. It has a “Hozelock” compatible connection on the outlet for connecting directly to a hose pipe (but this must be open ended). This model is often used for washing chemical toilets on caravan sites, amongst other low flow applications.
Model DC15F257 is for use with swan-neck type laboratory taps. The existing nozzle on the tap is removed, and replaced with the DC Pipe Interrupter which features its own integral nozzle. A short length of hose pipe can be connected to the tap for filling test tubes etc., but again the hose must be open ended. This model of Pipe Interrupter also features a clutch mechanism, which mechanically locks the DC15F257 in place once it has been fully screwed on to the lab tap, preventing it from being removed.
Finally, model DC20F257 has ¾” threaded connections and is predominantly used for topping-up swimming pools.
The vast majority of Fluid Category 5 applications are going to need a Break Tank and Booster Set, such as our “Boost-A-Break” range, to ensure there is a sufficient flow and pressure for the intended use. However, DC Pipe Interrupters can be a very useful solution for the low flow applications listed above. If you are unsure of which backflow prevention device is best suited to your application, then please contact us to discuss the requirements of your project.
To summarise…
DC Pipe Interrupters provide Fluid Category 5 “back siphonage” protection, but no “back pressure” protection.
They cannot have any restrictions fitted downstream of them, as this will result it water dispensing out of the vent holes.
They are only suitable for low flow and low pressure applications, that have an open outlet.
If you need any further information on this topic, or any other technical help, please feel free to give the Arrow Valves office a call or send us a message with any questions you may have.
