Plumbing: simple procedures in laboratory

A fault in the plumbing of the laboratory (a dripping tap, a blocked sink, etc.) can hamper laboratory work considerably. Some simple remedies are described below, in case a plumber is not readily available.

Fig. 2.15 Tools and materials for plumbing repairs

1. Tools and materials (Fig. 2.15)

● Adjustable wrench

● Pipe wrench

● Set of screwdrivers

● Bottle brush

● Rubber washers for taps

● Rubber stoppers such as those used in penicillin bottles

● Plunger for clearing blocked pipes

● Tow and jointing compound for sealing joints, if available.

Important: Before starting any plumbing operation, cut off the water at the mains.

2. Taps

A tap is made up of two parts (Fig. 2.16):

— the body (B), through which the water flows

— the head (H), which controls the flow of water by means of a rubber washer (W).

Between the head and the body, there is a joint ( J) of rubber or tow.

Fig. 2.16 Components of a tap

B: body; H: head; J: joint; W: washer.

Fig. 2.17 Removing the head of a tap

What to do if water flows when the tap is turned off

If water continues to flow when the tap is turned off, the washer needs to be replaced.

1. Unscrew the head of the tap using an adjustable wrench (turn in an anticlockwise direction) (Fig. 2.17).

2. Remove the worn washer from the base of the head (B). If the washer is embedded (Fig. 2.18(a)), pull it out. If it is screwed on (Fig. 2.18(b)), unscrew it.

3. Replace it with a new washer of the same type.

4. If the tap continues to leak after the washer has been re- placed, the seating (S) that receives the washer (Fig. 2.19(a)) is probably faulty. In this case place a rubber stopper in the hole (Fig. 2.19(b)).

This will act as a temporary seal until a plumber can be called in.

Fig. 2.18 Removing the washer

B: base of the head of the tap.

Fig. 2.19 Repairing the seating for the washer

S: seating.

What to do if water leaks out of the head of the tap

If water leaks out of the head of the tap, the joint needs to be replaced.

1. Unscrew the head of the tap using an adjustable wrench.

2. Replace the joint with a new one of the same type. If the joint is made of tow:

1. Remove the old joint, scraping the screw thread with a pointed knife (Fig. 2.20).

2. Wind new tow around the screw thread, starting at the top and winding in a clockwise direction (Fig. 2.21).

3. Smear jointing compound over the tow (Fig. 2.22).

4. Replace the head of the tap on the body and screw down as far as it will go.

Replacing the whole tap

Unscrew the faulty tap, using a pipe wrench (turn in an anticlockwise direction). Take the new tap; the body ends in a large screw (S) (Fig. 2.23(a)). Wind tow around the thread and smear with jointing compound as described above.

Fig. 2.20 Removing the tow from around the screw thread

Fig. 2.21 Winding new tow around the screw

Fig. 2.22 Applying jointing compound to the tow

Fig. 2.23 Replacing a tap

S: screw.

Screw the new tap into the water pipe in the wall in place of the old one (Fig. 2.23(b)). Tighten with the wrench.

2.3.3 Sink traps

Components of a sink trap (Fig. 2.24) The sink trap consists of:

— the body, fixed to the sink outflow by a joint ( J1);

— the swan neck of the U-shaped trap, fixed to the body by a joint ( J2).

The whole trap is attached to the waste pipe by a joint ( J3).

The wastewater flows into the trap, which is permanently filled with water (the seal). This prevents foul air from the waste pipes and sewers from coming up into the sink. Sink traps may become blocked so that wastewater from the sink or basin cannot drain away.

Fig. 2.24 Components of a sink trap

J1, J2, J3: joints.

Unblocking with a plunger

Place the plunger over the waste pipe. Let a little water flow around it to help it stick. Press down on the wooden handle to flatten the plunger (Fig. 2.25).

Pull it up and then push it down hard again. Repeat this procedure several times, as fast as you can. The suction caused may break up whatever is blocking the sink.

Unblocking with chemicals Use a commercial product intended for the purpose. Al- ternatively, use 250 g of sodium hydroxide pellets. Put the pellets in the bottom of the sink or basin, over the waste

Fig. 2.25 Unblocking a sink with a plunger

pipe. Pour 2 litres of boiling water on to the pellets (avoid splashing). Leave for 5 minutes, then rinse the sink thoroughly with cold water from the tap.

War ning: Sodium hydroxide solution is highly corrosive and should be used with extreme care. If it is splashed on the skin or in the eyes, wash the affected areas immediately with large quantities of water.

Unblocking by emptying the sink trap

Place a bucket beneath the trap. Unscrew joint J2 using an adjustable spanner (Fig. 2.26).

Clean the trap with a bottle brush or piece of wire. Clear away all waste material. If there is a white deposit (limescale) in the trap, take it apart completely. Heat the components in diluted acetic acid (20 ml of acid per litre of water).

Reassemble the sink trap.

What to do if the sink trap is leaking

If foul smells come up through the waste pipe of the sink, the permanent reservoir of water (the seal) at the bottom of the trap must have leaked because of a fault in joint J2. Screw the joint down tightly, or replace it with a new one (Fig. 2.27).

Important: Never pour strong acids down a sink, since they can cause corrosion.