What size vacuum pump do I need for my chamber?

Size on three numbers, not one: chamber volume, the pressure you need to reach, and the pump-down time you can accept. Pumping speed alone will mislead you, because a pump running near its ultimate pressure moves almost no gas.

Here is the part that catches people. A pump's rated speed — say 40 m³/h — is its speed at atmosphere. As pressure falls, the speed curve rolls off, and near the pump's ultimate pressure it approaches zero. So the last decade of pressure always takes disproportionately long. If you size only on volume ÷ speed, your calculated pump-down time will be optimistic by a large factor.

For a rough first pass on a leak-tight chamber in the rough-vacuum range, pump-down time scales with volume divided by speed, multiplied by the natural log of the pressure ratio you are crossing. The practical consequence: doubling the pump speed halves the time, but asking for one more decade of pressure costs you another full time constant. Decide which you actually need.

Then check the things that decide whether the pump survives your process, because these void the calculation entirely: gas ballast if you pump water vapour or solvents, corrosion-resistant construction for chemistry, inlet flange size (KF/ISO) matched to your pipework, motor voltage and phase, noise level if people work next to it, and the oil grade — mineral, PFPE, or a hydrocarbon-compatible synthetic.

The other thing that dominates real installations: pipework and leak rate. A long, narrow inlet line can throttle a large pump down to a fraction of its rated speed, and a chamber with a real leak will settle at the pressure where the leak rate equals the pump's throughput — no amount of extra pumping speed will get past it. If a chamber will not reach the pressure the calculation predicts, measure the leak rate before buying a bigger pump.

If you send us chamber volume, target pressure, acceptable pump-down time and what you are pumping, we will do this sizing and come back with the models that fit, including what the last decade is going to cost you in time.