The simplest tap is a tapered wooden plug pushed into a pipe opening, but at 10 m of head the water pushes a 20 mm plug out with about 31 N and a 40 mm plug with about 123 N, so it needs a tight taper or a pin to stay in place. A salvaged gate valve or a carved hardwood rotating-plug tap is more reliable, and any tap should be closed slowly, because a quick closure on a moving line can add about 3 bar.
A tap or valve opens and closes the flow of water. In a gravity system with no pumps the choices are limited to what you can salvage or carve, and the force of the water, which grows with head and bore, decides which will hold.
What The Parent Page Offers
- A plug valve: a wooden plug pushed into a pipe opening; pull it out to flow, push it in to stop. Crude, but effective.
- A gate valve salvaged from plumbing supply.
- A wooden barrel spigot inserted into the pipe.
- A carved hardwood tap with a drilled bore and a rotating plug.
How Hard The Water Pushes On A Plug
Force = pressure × area, with pressure = ρ × g × h and area = π × d² ÷ 4. Inputs: ρ = 998 kg/m³, g = 9.81 m/s², head h.
20 mm plug at 10 m head.
- Pressure = 998 × 9.81 × 10 = 97,900 Pa.
- Area = π × 0.01² = 3.14 × 10⁻⁴ m².
- Force = 97,900 × 3.14 × 10⁻⁴ = 30.8 N, about 31 N or 3.1 kg-force.
40 mm plug at 10 m head. Area = π × 0.02² = 1.26 × 10⁻³ m²; force = 97,900 × 1.26 × 10⁻³ = 123 N, about 12.5 kg-force.
At 20 m head the forces double: 61.5 N and 246 N. A plug held only by friction in a plain hole will creep out under that load, and a wet plug swells and shrinks. So taper the plug and the hole, drive it firmly, and fit a pin, wedge or cord to hold it, especially in bores over 25 mm or on heads over 10 m.
A Rotating-Plug Tap
The parent page’s carved tap works like a cock: a tapered plug turns in a tapered seat, with a hole drilled across the plug.
Step 1: Choose a hard, close-grained wood for the body and plug.
Step 2: Drill the through bore in the body for the pipe connection, and ream a tapered seat across it.
Step 3: Turn a tapered plug to fit the seat, and drill a cross hole in it of the same bore as the pipe.
Step 4: Grease the plug with tallow or beeswax, seat it, and fit a handle and a retaining washer or pin so it cannot be pushed out.
Step 5: Turn it a quarter turn to open and close; check it for leaks and swelling after the first wetting.
Close Slowly
A tap closed fast on a moving line makes a pressure surge. Tap Types gives about 3 bar for a ball valve slammed shut on a line running at 1 m/s, and gate valves surge less because they take many turns to close. A quarter-turn tap is quick to close, so close it with a steady hand. Surges are a danger to wooden, bamboo and clay pipe, which have low limits (Pipe Materials & Construction).
Choosing
| Tap | Strength | Weakness |
|---|---|---|
| Wooden plug | No parts; made on the spot | Pushed out by head; leaks as the wood moves |
| Barrel spigot | Made for liquids | Small bore; wear |
| Carved rotating plug | Quarter-turn, holds pressure when well fitted | Needs skill; swells |
| Salvaged gate valve | Slow closing, standard fit | Needs salvage; seals wear |
| Salvaged ball valve | Quick, tight | Quick closure surges the line |
If you salvage brass fittings, flush them well before use: old brass can contain lead as I recall it, and lead dissolves into drinking water.
Fit Taps Above The Basin
The spout ends above the rim of the sink or basin with an air gap, and no hose is left on it (Plumbing Separation).
Common Mistakes
- A bare friction plug on a high-head line. It blows out.
- Slamming a valve shut.
- Not pinning a plug.
- A tap that drips constantly, wasting water and wetting the ground.
Safety
A blown-out plug can cause injury, and a surge can burst the pipe
A 123 N plug leaving a pipe end at 10 m of head can hit a hand or face. Do not stand in line with a plug when opening a high-head line, and pin plugs. Close valves slowly. Flush salvaged brass and avoid lead-containing parts in the drinking line.
What’s Next
- Learn next: Indoor Plumbing Layout — place the taps in a house
- Combine with: Isolation Valves — shutoff valves for branches