A high-pressure hot water (HPHW) circulation pump has to move a large flow of 120°C water against a modest head, with a seal and casing that suit the temperature. For an ammonia stripping plant at a landfill, the pump chosen was a horizontal end-suction pump delivering 65 litres per second at 5 bar, driven by a 55 kW motor.
The challenge: hot water in a closed loop
The plant’s heat is carried round a closed circuit of pressurised hot water. The circulation pump keeps the water moving through the heat source and heat users. If it stops, the plant loses its heat supply. The water is at about 120°C with 12 bar at the pump suction, so the pump must be built for that pressure and temperature, and it needs to run continuously.
The approach: match the duty, then the details
The duty
| Item | Value | What it means |
|---|---|---|
| Flow | 65 l/s (about 234 m³/h) | The circulation rate through the loop |
| Temperature | 120°C | Sets seal and material choices |
| Suction pressure | 12 bar | The loop is pressurised to keep the water liquid |
| Differential head | 5 bar | Only the loop’s resistance, not a lift |
| Motor | 55 kW, 2,900 rpm, IP56 | Tropicalised for a humid climate |
The hydraulic power is the flow times the pressure rise: 0.065 m³/s x 500 kPa is about 33 kW. A 55 kW motor gives headroom for pump efficiency and operating margin.
The construction
The pump is in steel and ductile iron with a chrome steel shaft and a single mechanical seal, driven through a flexible coupling and mounted with its guard on a fabricated base frame. The frame lets the pump and motor be delivered aligned.
A spare in the same family
For another pair of lines, the quotation was for a bare-shaft pump of a similar family, in ductile iron with a stainless steel impeller and shaft and an air-cooled mechanical seal. Bare-shaft means no motor or base is supplied, which suits a site that already has a motor and frame. The air-cooled seal suits hot water without a separate cooling water supply.
The small pump that keeps the loop pressurised
A separate quotation covered pressurisation pumps: vertical multistage pumps in pressed 304 stainless steel with a 1.1 kW motor. They top up the loop pressure so the water stays liquid at temperature.
Why it works
High flow at low head favours a single-stage end-suction pump. Long lead times (16 to 18 weeks from the UK, and up to 22 weeks delivered for the bare-shaft pump) are the main risk, which is why a spare is worth holding.
What to consider for your own project
- State flow, temperature and suction pressure, not only head.
- Check the seal type for hot water.
- Decide between a complete set and a bare-shaft pump.
- Plan for lead time. Four months is normal.
- Do not forget the pressurisation pump.
For other plant spares planning, see our post on fan impellers and shafts as spares.
FAQ
What is an end-suction pump?
A pump where liquid enters along the shaft axis and leaves at right angles, common for general duties.
Why is head low but pressure high at the suction?
The loop is pressurised to keep hot water from boiling. The pump only overcomes the loop’s resistance.
What is a bare-shaft pump?
A pump supplied without a motor or baseplate.
What does tropicalised mean?
The motor is protected for hot, humid conditions.