The water that discharges from a tap should come out with sufficient force (i.e. the force you would expect from a normally working tap). Some taps are undoubtedly better than others, with a greater flow or pressure, but in general we know what to expect. Therefore, when faced with a tap with a poor water flow rate, we can surmise that something is wrong.
Before condemning the whole system of pipework, consider that it may be the tap itself that is faulty. Does it operate freely and open fully? Look at the pipework and see what else is served from the same section, and check out these taps or outlets too.
Are they also suffering this lack of flow? If so, has the problem been getting slowly worse or is it a sudden drop in pressure or flow? Clearly, if several taps are affected, there is some form of blockage in the pipeline that must be removed.
Figure 4.13 Replacing the ‘O’ ring in a tap with a swivel spout
Such a blockage will generally be one of the following:
C
C A turned-off or closed-down water supply C
C A blockage due to debris in the storage cistern C
C A plug of ice C
C An airlock C
C Corrosion or limescale build-up
The first thing to do in this situation is look for the source of the water that is being blocked. If the problem occurs suddenly, affecting the cold water mains supply to the kitchen sink tap, possibly with the flow stopping completely, it may be worth phoning your water supplier as they may have turned off the water for some reason.
For your low-pressure pipework, such as that serving the hot and cold taps to the bathroom, check whether the storage tank in the loft is full of water. Is the lid in place? Ensure that vermin have not got into the vessel, drowned and sunk to the bottom, blocking the outlet pipe.
The weather will be a good indicator of whether a blockage might be due to ice. This scenario is discussed later. The
problems of airlocks, corrosion and limescale, however, may not be so obvious and are discussed in more detail below.
BLOCKAGES CAUSED BY AN AIRLOCK
When an airlock is suspected to be the cause of a lack of water flow to a tap, the air must be forced from its trapped location. An airlock is the result of poor plumbing design in a low-pressure (storage-cistern-fed) system. When running pipework, you should never run it uphill and then downhill, because air will accumulate in the high pocket (see Figure 4.14). With air trapped in the high pocket, no water can pass if the water pressure is insufficient. You should aim to design your system so that air within can always rise and escape through a tap outlet or via the cold feed or open vent pipe.
With a badly designed system with high points, once the air has been expelled from these high points it allows water to flow, so the problem generally only recurs when a system has been drained down. If you didn’t install the plumbing system
yourself, you won’t know whether it was installed correctly, therefore, as an unsuspecting individual who has drained down the pipework, you have no idea that this will occur until you try to refill the system. So, let’s say you have turned on the water supply after draining down for some reason and there is no water flow at the outlet. You simply do not know where the high point is that is causing the trapped air, so what do you do?
The first thing to try is to open the tap and, either using a hose connected to its outlet or positioning your mouth around the spout of the tap, try to give a good blow. What this sometimes does is blow a bit of water that was lying inside the pipe up, forcing itself past the trapped air which can then escape back out of the system, via the cold feed. A variation of this is to get a small length of hosepipe and pass it down into the storage cistern and into the cold water pipe feeding the offending section of pipework. With the hose in place and with the tap opened, you can now blow with all your might in the hope of forcing the water past the trapped airlock.
Failing this, try a trick used by many plumbers. Get a small piece of hosepipe and join the cold high-pressure mains water tap outlet to the low-pressure tap outlet and use this water
total blockage due to trapped air
partial blockage storage cistern
Figure 4.14 Common causes of airlocks
pressure to force the air from the high section. This trick works, but note that technically you would be in violation of the Water Supply Regulations unless you had some means of backflow in place to ensure that contaminated water could not flow back into the water authority mains.
BLOCKAGES DUE TO CORROSION OR SCALE BUILD-UP
Limescale build-up is a problem that has already been discussed, but recognizing it is not always easy. It is generally accepted that both corrosion and scale build-up occur gradually over a long period, during which time things slowly get worse.
The type of metal used will indicate the likelihood of pipework suffering from corrosion. Galvanized iron pipes in particular can be a problem and, if you have these, you should always suspect them of causing a reduced water flow rate. For example, where galvanized iron has been used in conjunction with copper or brass, electrolytic corrosion occurs, creating encrustations within the pipe. The worst-affected point would be where the two dissimilar metals join together. Fortunately, galvanized iron is no longer used for domestic pipework and therefore this problem will only occur in older dwellings. Electrolytic corrosion is discussed in Chapter 6.
Key idea
There is the greatest possibility of a blockage due to corrosion where you see copper or lead pipe connected to steel pipework. The jointing of the two dissimilar metals is likely to lead to electrolytic corrosion.
A blockage caused by limescale is not as easy to detect and is only a problem in hot water systems. The point where the blockage may be worst is within the pipe exiting the top of the hot water storage cylinder. If you isolate the water supply to this cylinder and remove the pipe coming from the top dome of the cylinder to inspect it, you may find limescale blocking the pipe.
This is where the hottest water is found and therefore it is here that limescale is most likely to form. (Figure 1.10 shows a fitting blocked by limescale.)