Cold-climate design

What actually freezes, and why it matters

Work through a ram in a hard frost and the picture is reassuring. The waste valve keeps clacking, water keeps moving through the body, and the moving water in the drive pipe carries heat up from the ground. A ram that is running is remarkably frost-resistant; the failure is almost always what happens when it stops.

• A full, closed pipe splits. Water expands about 9% on freezing, and the pressure that generates is far beyond any pipe's rating. A pipe that is full, sealed at both ends and exposed will burst — and it will burst at the weakest point, which is usually a fitting or a joint rather than the pipe itself.
• Water that can drain does not split. This is the whole basis of freeze protection: an empty pipe is a safe pipe.
• The ram body is usually safe. Cast or heavy metal bodies and hard-working valves rarely suffer, because the machine is either running or drained.
• Ice in the wrong place is the real hazard. Ice at the outfall builds a dam, backs up the waste stream, and can flood or bury the ram. Ice at the intake starves the drive pipe of flow.

Find your local frost depth — the maximum depth to which the ground freezes — from your building authority, agricultural extension service or a local contractor. Every burial recommendation depends on it, and it varies from a few centimetres to well over a metre.

Designing for the freeze

1 · Bury the pipes below the frost line

Both the drive pipe and the delivery pipe should be laid below the local frost depth wherever they run through ground that freezes. This is far cheaper done with the trench open than retrofitted, and it is the single most effective measure. Where a pipe must come above ground — at the intake, at the ram, over a rocky outcrop — treat that exposure as the design problem and protect it specifically.

2 · Arrange for it to drain

Give every exposed section a way to empty itself. Slope the drive pipe and the delivery pipe continuously back to a drain point, and fit drain valves at the low spots. Then "winterising" a ram that must be stopped is a matter of opening two valves rather than dismantling anything. Take particular care with the delivery pipe: it rises steeply and is often left full during a shutdown.

3 · Keep it running if you possibly can

The cheapest freeze protection is to not stop. A ram that keeps beating keeps water moving through the machine, keeps the waste stream flowing away from the outfall, and keeps the intake clear. If the demand drops in winter, resist the temptation to shut the ram down — instead let it fill the tank and overflow, or divert the delivery. Continuous operation is what a ram is for.

4 · Shelter the machine, but keep it serviceable

• Insulated box: a hinged, insulated enclosure around the ram keeps the wind and the worst of the frost off while keeping the valves reachable. Leave it removable rather than built in — you will need access.
• Earth sheltering: setting the ram into a recess with the spoil banked around it uses the ground's warmth. Ensure drainage so the recess does not collect meltwater.
• Straw bales, mulch, snow: old methods that work well. A deliberate snow blanket over the enclosure is good insulation — do not clear it away.
• Never seal a wet space completely. A watertight, airtight box traps moisture and creates a corrosive, uncomfortable environment to service. Ventilation matters more than perfect insulation.

5 · The air chamber and the valves

The delivery vessel contains both water and air, and the water in it can freeze. Insulate it, and give it a drain plug so it can be emptied during a long shutdown. Small-bore fittings, snifter holes and gauge tappings freeze first because of their small thermal mass — keep them inside the shelter or drain them. When you do shut down, open the valves and drain the vessel rather than relying on insulation alone.

6 · The outfall and ice dams

This is the winter failure that is easiest to overlook. The waste stream leaves the ram and drops into a drainage channel; in cold weather that channel freezes from the edges inward, ice builds up, and the outfall backs up until water is pooling around the ram's foundation — which is precisely the scour problem described on Reliability, delivered by winter instead of by design.

• Keep the waste stream moving, and carry it well clear of the foundation.
• Size the outfall for ice, not just for water — a generous, steep, smooth channel is less likely to dam.
• Do not let the outfall discharge into a spot where meltwater will pond against the pad.

7 · The intake

• Keep it submerged below the ice but off the bed. Drawing from close to the bed in winter pulls sediment; drawing at the surface lets the intake freeze into the ice sheet.
• Watch for anchor ice. In very cold, turbulent streams, ice forms on submerged stones and screens, blocking them. A slightly deeper or larger intake helps; a spring-fed intake avoids the problem entirely.
• Clear snow from the approach, but leave the screen accessible — the intake is the thing you will be clearing most often in winter.

If it does freeze, and restarting

Assume a frozen pipe is a damaged pipe and check it rather than simply thawing it. Ice that expanded has already stressed every fitting between the blockage and the nearest closed valve.

1. Find the ice, do not guess

   Tap along the pipe and feel for the solid, dead section. Ice usually forms at the most exposed point — a fitting, a bend, or where the pipe leaves the ground.

2. Thaw gently, with warm water or a heat mat

   Pour warm — not boiling — water over the outside, working from the downstream end back toward the blockage so meltwater can escape. Never use a blowtorch or a naked flame on a pipe, and never strike a frozen pipe to break the ice.

3. Inspect before you pressurise

   Look for splits, weeping joints and distorted fittings. Replace damaged sections. A split that is pressurised after a thawing repair will fail again, usually somewhere worse.

4. Clear the intake and outfall first

   Restarting with a blocked intake produces a weak, erratic beat that looks like a valve problem; restarting with a dammed outfall backs water up around the machine. Clear both before you touch the valves.

5. Re-charge and re-tune

   A long shutdown lets the air chamber lose its cushion, and a cold machine tunes differently. Expect to re-charge the chamber and re-tune the beat once it is running again.

Winter and drought flow variation is also covered on Installation, and the general service routine is on Maintenance.