Ram Pump

Part of Water Systems

How to build and operate a hydraulic ram pump — a device that uses the energy of falling water to pump a portion of that water to a greater height, with no external power.

Why This Matters

The hydraulic ram pump is one of the most remarkable devices in the engineer’s toolkit: it pumps water uphill using no fuel and no electricity. Its only power source is the kinetic energy of water flowing downhill from a source — and it uses that energy to lift a portion of the water even higher than the source. A properly built and installed ram pump runs continuously for months or years with virtually no maintenance.

The ram pump was invented in the late 18th century and spread rapidly because it solved a fundamental problem: many communities sit above their nearest reliable water source. A river runs through a valley below; the village is on a hillside. A ram pump installed at the river can lift water 20–50 meters uphill to fill a tank serving the village, using nothing but the river’s flow.

The tradeoff is efficiency: a typical ram pump delivers 10–20% of the input water to the elevated output. The remaining 80–90% flows away as waste water. This is acceptable when the source stream is large relative to the community’s needs.

How It Works

The ram pump operates on water hammer — the pressure spike that occurs when a moving column of water is suddenly stopped.

Operating cycle (approximately 20–100 cycles per minute):

1. Drive valve open: Water flows from the source down the drive pipe, accelerating as it fills the pipe
2. Drive valve closes: When flow velocity becomes high enough, the waste valve (a spring-loaded flapper) snaps shut under the force of the moving water
3. Pressure surge: The momentum of the moving water column creates a powerful pressure spike in the pump body — far above the static head of the supply
4. Delivery valve opens: The pressure spike exceeds the head of the delivery column; the delivery valve (a check valve) opens and a burst of water is forced up the delivery pipe
5. Air chamber absorbs surplus: Surplus pressure energy is stored in a compressed air chamber, smoothing flow in the delivery pipe
6. Pressure drops: The pressure spike decays; the delivery valve closes; the waste valve opens under spring force; cycle repeats

The elegance is that all valves are passive — they operate automatically from pressure differences, requiring no human intervention.

Component Design

Drive Pipe

The drive pipe carries water from the source to the pump body. Its length and diameter determine pump performance.

• Material: Any pressure-resistant pipe — iron, clay (with care), or bamboo for small installations
• Length: Minimum 5× the head from source to pump. For 2 m of head at the source, minimum 10 m of drive pipe. Longer is better — longer drive pipe = more momentum = stronger water hammer = higher delivery pressure.
• Diameter: 50–100 mm for most applications. Larger diameter = more flow = higher output
• Slope: Install at consistent downhill grade. Avoid bends and high points (air accumulates there)

Pump Body

The valve chamber where water hammer occurs. Must be strong — pressure spikes can reach 10× supply head.

Construction materials for a medium-duty pump (2–5 m head, delivery to 30 m):

• Cast iron is traditional and ideal
• Fabricated steel is adequate
• Thick-wall clay or ceramic can work for low pressures but is fragile

Internal volume: Approximately 2–3× the volume of one pump cycle. For 50 mm pipe pumping at 60 cycles/min, this is roughly 1–2 liters.

Waste Valve (Impulse Valve)

This valve must open freely when water flows and snap shut under the hydraulic impulse. It is the most critical and most wear-prone component.

Simple construction:

• A flat rubber or leather disc resting on a machined brass or iron seat
• The seat is a flat ring with a central hole (25–40 mm diameter)
• The disc is held loosely by a guide pin through its center
• No spring is needed for the basic design — gravity closes the valve
• Optional: a light spring to adjust the closing force (heavier spring = more flow before closure = stronger impulse = higher delivery head)

Travel: The disc must travel 10–15 mm to open fully. More travel = slower cycle = more flow per cycle.

Delivery Check Valve

Opens under high pressure, closes when delivery pressure exceeds supply pressure. A standard ball check valve or spring-loaded disc valve. Must withstand the full delivery head continuously.

Air Chamber

A sealed chamber above the delivery check valve, partially filled with air. The compressed air acts as a spring, smoothing the pulsating output into steady flow.

• Volume: 5–10× the volume of one delivery pulse
• Initial air charge: 40–60% of chamber volume
• The air volume decreases over time as air dissolves into water. Provide a small cock to re-inject air periodically (or an automatic snifting valve — a tiny hole near the delivery valve that admits a bubble of air each cycle).

Delivery Pipe

From the air chamber to the storage tank above. Any pipe material that can handle the delivery pressure.

• Delivery pressure = supply head × (delivery height / supply head) approximately — but actual output head is governed by valve spring tension and air chamber pressure
• Maximum delivery head in practice: about 10× the supply head for a well-designed pump

Installation

Site selection criteria:

1. A stream or spring with reliable year-round flow
2. At least 0.5 m of vertical fall between source and pump site (more is better — 1–3 m is typical)
3. Flow rate at source: minimum 3–4× the desired delivery flow
4. A tank or distribution point at least 5 m above the pump site (higher is fine)

Installation steps:

1. Build a collection chamber at the source — a small masonry box with an overflow, keeping the water level constant
2. Install the drive pipe from collection chamber to pump site — bury or protect from frost damage
3. Mount the pump body on a concrete or masonry base — it will vibrate with each cycle
4. Connect the drive pipe to the pump inlet, delivery pipe to the air chamber outlet
5. Anchor the drive pipe at both ends and at least every 3 m along its length — water hammer creates strong pipe forces
6. Run delivery pipe to the storage tank — this can go up steep slopes, around obstacles
7. Install a waste water drain from the waste valve — this flows continuously when the pump runs, at 80–90% of input flow

Starting the pump:

1. Fill the drive pipe with water
2. Open the collection chamber inlet
3. Hold the waste valve open manually while the pipe fills
4. Release the waste valve — it will begin cycling on its own
5. If it does not start, slightly compress the waste valve spring (or add a small weight) to increase sensitivity

Performance and Optimization

Typical performance:

• Supply head 1 m, delivery head 10 m: efficiency ≈ 10–15%
• Supply head 2 m, delivery head 20 m: efficiency ≈ 12–18%
• Supply head 3 m, delivery head 30 m: efficiency ≈ 15–20%

Cycle rate: 30–100 cycles per minute is normal. Very fast cycling (>100/min) means the waste valve is too light — add weight. Very slow cycling (<20/min) means too heavy — reduce weight or spring force.

Maximizing output:

• Lengthen the drive pipe (more momentum)
• Increase drive pipe diameter (more mass per cycle)
• Reduce delivery head (less work per cycle)
• Use multiple pumps in parallel for higher total flow

Common problems:

Problem	Likely Cause	Fix
Pump won’t start	Air in drive pipe	Re-fill pipe, bleed air
Pump stops after running	Drive pipe leak, air pocket	Check joints, re-prime
Low delivery flow	Air chamber waterlogged	Re-inject air via cock
Waste valve won’t close	Valve seat worn or dirty	Clean or re-face seat
Excessive vibration	Loose mounting	Re-anchor to base

A well-built ram pump installed at a reliable source will run for 5–10 years before the waste valve needs replacement. The rest of the system — pipes and air chamber — should last decades. Keep a spare rubber disc for the waste valve; that one part is the consumable that makes everything else possible.