Section 40 · Reference
Glossary
The vocabulary of rams — the words Victorian millwrights, development engineers and YouTube builders all use, sometimes for the same part.
- Air chamber · pressure vessel, air vessel, cushion tank
- Sealed vessel above the delivery check valve holding trapped air that cushions the slam, smooths delivery flow, and keeps pushing water between beats. Loses its air gradually to dissolution; see recharging.
- Beat · cycle, stroke
- One complete operating cycle of the ram — charge, slam, delivery, recoil. Small rams beat roughly 30–100 times per minute.
- Bélier hydraulique
- French for "hydraulic ram" — Montgolfier's original name for the device in 1796.
- Clack valve · waste valve, impulse valve
- The weighted or spring-loaded valve that opens to let water accelerate and slams shut to trigger the hammer. The ram's throttle and its ignition switch in one.
- Compound ram
- A ram with separated drive and delivery circuits, allowing potable water to be pumped using non-potable drive water.
- D'Aubuisson efficiency
- Energy efficiency measured against all water passing through the ram: q·h/(Q·H). Typically 60–80% for a healthy ram. See Physics.
- Delivery check valve · NRV, non-return valve
- The one-way valve that admits water to the air chamber during the pressure spike and reseats when pressure falls, holding the uphill column.
- Delivery head · lift, h
- Vertical rise from the ram to the delivery tank's water surface. Horizontal distance costs only friction, not head.
- Drive flow · Q
- Total water flowing through the ram per unit time — delivered flow plus waste flow.
- Drive head · fall, supply head, H
- Vertical drop from the source water surface to the ram. The ram's power supply, measured in metres.
- Drive pipe · supply pipe, impulse pipe
- The rigid pipe from intake to ram, ideally 3–7× the fall, constant diameter, as straight as practical. Its inertia is the engine's flywheel.
- Drive tank · forebay, fosset, header tank
- Small settling tank at the source that houses the screened intake and steadies the supply.
- Hydram
- Contraction of "hydraulic ram" — the ram pump itself.
- Joukowsky equation
- Δp = ρ·c·Δv: the pressure rise when a water column is stopped abruptly. The reason a 2 m fall can pump to 20 m. See Physics.
- Lift ratio
- Delivery head ÷ fall (h/H). Sweet spot 2–6:1; workable to about 10:1.
- Papa Pump
- Modern commercial ram using a concentric venturi waste valve (F. P. Selwyn, patented 1996/2001).
- Rankine efficiency
- Figure of merit counting only the rejected water as input: q·h/((Q−q)·H). Always ≥ D'Aubuisson; can exceed 100% at low lift ratios, so it is not a true efficiency.
- Recoil
- The pressure rebound after the delivery phase; the reflected suction wave that helps the waste valve reopen and resets the beat.
- Snifter · snifting valve, air recharge
- Tiny hole or valve near the delivery check that inhales a bubble of air each beat, replenishing the air chamber.
- Static head
- Pressure exerted by a still water column: ~0.098 bar per metre. The benchmark the spike must beat at the delivery valve.
- Volumetric efficiency
- Fraction of source water actually delivered: q/Q ≈ η·H/h. Typically 5–20% — the rest is the fuel.
- Waste flow · spent flow
- Water leaving through the waste valve: Q − q. Clean water, returned below the ram — ideally re-used.
- Water hammer · hydraulic shock, "knocking"
- The pressure transient when moving water is stopped suddenly. Household nuisance; ram power source.
- Wave speed · c, celerity
- Speed of the pressure wave in the pipe: ~1200–1400 m/s in rigid steel, 300–500 m/s in PVC. Sets the valve-timing mathematics.
- Waterlogged chamber
- An air chamber whose cushion has dissolved away. Symptoms: banging delivery line, harsh slams. Cure: recharge the air.