Section 23 · Design & Build
Build your own ram pump
The classic DIY ram — two brass check valves, a tee, a pipe for an air chamber — has been built in thousands of versions since university extension services first published the pattern. Here's a faithful 2-inch build.
On this page
The schematic
Parts & tools (2-inch build)
| Part | Quantity | Notes |
|---|---|---|
| 2″ brass swing check valves | 2 | One becomes the waste valve (add a weight arm), one the delivery check. Buy the same type twice — spares interchange. |
| 2″ tee, threaded | 1 | The body. Some designs use a second tee for the chamber junction. |
| 2″ → 1″ reducing bushings / tees | as needed | For the delivery riser and chamber base. |
| Air chamber | 1 | 3″–4″ × ~600 mm pressure-rated pipe with rated caps, or a small steel tank — roughly 3–5 L of air. (A 600 mm length of 2″ pipe holds only about 1.3 L, usually too little cushion.) Never thin-wall DWV pipe. |
| Snifter | 1 | A ~1 mm drilled hole near the delivery check's inlet side, or a Schrader valve for manual recharging. |
| Weight hardware | assorted | Bolt through the waste-valve flap with washers/nuts so the effective weight is adjustable along the arm. |
| Nipples, unions, ball valves | as needed | Unions at drive and delivery let you service the pump; a ball valve on the delivery makes starting easier. |
| Thread sealant / PTFE tape | 1 | Every joint — the drive side must be airtight as well as watertight. |
| Tools | — | Two pipe wrenches, drill & 1 mm bit, hacksaw, tape measure. |
Typical parts cost: roughly US$60–150 depending on region and valve quality. Stainless or bronze valves last longest; the cheapest zinc valves are the first thing you'll replace.
Assembly
Prepare the valves
Open both check valves and inspect the rubber facings. To the waste valve's flap, bolt a weight arm (bolt + washers + lock nut) so its position along the flap is adjustable. The delivery check stays stock.
Build the body
Thread the drive inlet into one end of the tee's run and the waste valve onto the other, oriented so gravity holds its flap open. Seal every thread.
Add the delivery riser
From the tee's branch, reduce up to the delivery check valve so flow can only pass upward. Below it, the check sees the slam; above it, the chamber.
Fit the air chamber
Above the delivery check, branch to the vertical chamber (60 cm of 3″–4″ rated pipe with caps, or a steel vessel) and to the delivery outlet union + ball valve. Big and ugly beats small and lively — chamber volume is your friend.
Drill the snifter
A ~1 mm hole on the chamber side of the delivery check's seat area (or fit a Schrader + needle valve). Deburr it; it inhales a bubble of air each beat.
Mount it
Bolt the assembly to a concrete pad or heavy timber block. The waste valve needs free travel and the body must not flex — the beat is a hammer, and a loose pump walks.
Connect the drive pipe
Rigid, sloping down to the pump with no high points, through a union. Fill slowly from the source and watch for air spurting from the open waste valve — wait until the flow runs solid and steady.
Start it
With the delivery ball valve mostly closed, push the waste valve down and release it several times. After three or four pushes it should catch and self-cycle. If it stalls, purge more air and try again.
Tune the beat
Slide the weight until the beat is brisk but solid — roughly 30–100 beats per minute — and delivery (measured at the tank) is maximised. See below.
Commission
Open the delivery valve fully, check every joint dry-and-tight, channel the waste water away, and re-visit after a week to re-tune and re-check the chamber.
Tuning the beat
The weight on the waste valve is the only control that matters. Moving it toward the tip makes the valve heavier: the water must run faster to slam it, so beats are slower but harder — higher pressure, better for big lifts. Moving it inward gives faster, gentler beats for low lifts.
| Symptom | Meaning | Fix |
|---|---|---|
| Fast, fluttery beats, little delivery | Valve too light — weak hammer | Move weight outward (heavier) |
| Slow, laboured beats, then stall | Valve too heavy for the flow | Move weight inward (lighter) |
| Won't self-start | Air in drive pipe, or flow too small | Purge air; check intake submergence; lighten valve |
| Delivery line bangs | Waterlogged chamber | Recharge air (see Maintenance) |
| Best delivery is "meh" | Site limits, not tuning | Check ratio ≤ ~8:1 and fall ≥ 1 m; verify flow |
Safety
- Pressure-rated air chamber only. The slam can spike pressures tens of times the static head. Thin-wall drain pipe can burst violently. Steel, or pressure-rated pipe with a generous margin.
- Never stand over the chamber when the ram is beating, and never pressure-test with compressed air.
- Drain before hard frost — ice splits chambers and bodies with cheerful reliability.
- Eye protection when starting and tuning; the waste jet can throw grit.
Built and beating? The civil works — intake, trenching, anchor, commissioning — are in Installation. If it misbehaves later, the fix is usually in Maintenance.