Choosing the right pump and pipe diameter for the miner circuit

In the miner circuit one variable is fixed: the flow rate the manufacturer requires. Pipe and pump are sized for it, not the other way round. The values here are guide figures for planning; the datasheets of the miner and the pump are what counts.

The flow rate

Bitmain requires 8 to 10 litres per minute per unit for the S21 XP Hyd. For several units the value adds up:

• 1 unit: around 9 litres per minute
• 2 units: around 18 litres per minute
• 5 units: around 45 litres per minute
• 10 units: around 90 litres per minute

Take the value for your model from the manual.

The pipe diameter

The narrower the pipe, the faster the coolant flows and the higher the resistance. In heating pipe networks, 0.3 to 1.5 metres per second is the guide value for the flow velocity. Above that, pressure drop and noise rise sharply.

At around 1 metre per second this gives the following inner diameter:

• 9 litres per minute: about 14 mm
• 18 litres per minute: about 20 mm
• 45 litres per minute: about 31 mm
• 90 litres per minute: about 44 mm

Choose the next standard size up. The inner diameter is what matters: plastic pipes have thicker walls than metal pipes of the same nominal size.

The header is sized for the total flow rate, the branch to each unit for the flow rate of one unit.

The pump

A pump is described by two values: how much it delivers and against what resistance. The two are linked. The higher the resistance, the less it delivers. The datasheet shows this as a pump curve.

The resistance of the circuit is made up of four parts:

1. The miner's cold plates. The manufacturer states the pressure drop at the target flow rate.
2. The heat exchanger or dry cooler. It is in its datasheet.
3. Pipes and bends. With a correctly chosen diameter, the smallest part.
4. Filters and valves.

Add up the pressure drops at the target flow rate. The pump must reach exactly this point on its curve: the target flow rate at this total. Allow a reserve of 10 to 20%.

Three mistakes when choosing

Calculated with water, filled with glycol. Glycol is more viscous than water, especially when it is cold. The pressure drop rises, the pump delivers less. Size it for the actual coolant.

System pressure confused with pump pressure. The 3.5 bar that Bitmain states as the upper limit is the maximum pressure at the unit. The fill pressure of the system and the pressure of the pump together must stay below it.

Wrong material. The housings of standard heating pumps are made of grey cast iron or gunmetal. A circuit with aluminium cold plates calls for a pump made of stainless steel or plastic.

Several units

Each unit gets its own branch with shut-off valves and a balancing valve. This lets you set each unit to receive its target flow rate, and you can take a unit out without draining the circuit.

What else belongs in the circuit

• Filter upstream of the miner, with shut-off valves for cleaning
• Expansion vessel, because the coolant expands as it heats up
• Safety valve set below the permitted pressure of the miner
• Air vent at every high point
• Flow meter or flow switch per unit or per line
• Pressure gauge and thermometer on flow and return

The check after filling

Measure the flow rate before the miner starts. If it is not right, first look for air in the circuit and a clogged filter. Only after that is it down to the pump or the pipe.

Sources

• Bitmain: S21 XP Hyd, specifications with flow rate and pressure
• Baunetz Wissen: pipe network calculation, guide values for the flow velocity
• Dow: Dowtherm SR-1, physical properties of glycol mixtures (PDF)
• Wilo: product data of a heating pump, housing materials

As of October 2026. This article does not replace sizing by a specialist contractor.