A backing pump (also called a roughing pump) is a pump that exhausts a high-vacuum pump to atmosphere. Turbomolecular and diffusion pumps cannot discharge directly to atmosphere, so they sit on top of a backing pump – usually a rotary vane or scroll pump – which does the first stage of the work.
Why high-vacuum pumps need one
A turbomolecular or diffusion pump only works once the pressure is already low. The backing pump first roughs the system down from atmosphere, then keeps the turbo’s exhaust (the “backing pressure”) low enough for it to run. Without a backing pump, the high-vacuum pump simply cannot operate.
What makes a good backing pump
The backing pump must have enough pumping speed for the gas load and reach a low enough pressure for the high-vacuum pump. Common choices are two-stage rotary vane pumps (deep vacuum, low cost) or dry scroll pumps (oil-free, clean) – see scroll vs rotary vane.
Roughing vs backing
The same pump often does both jobs: “roughing” the initial pump-down from atmosphere, then “backing” the turbo during operation. Matching it correctly to the high-vacuum pump is essential – ask us to specify the pair.
Need a backing pump matched to your turbo?
Tell us your high-vacuum pump and application and we’ll specify the right backing pump. Email [email protected] or request a quote.
Frequently asked questions
What is a backing pump?
A backing (roughing) pump exhausts a high-vacuum pump such as a turbomolecular or diffusion pump to atmosphere. High-vacuum pumps cannot run without one.
What type of pump is used as a backing pump?
Usually a two-stage rotary vane pump (deep vacuum, low cost) or a dry scroll pump (oil-free, clean). The choice depends on the gas load and whether oil-free operation is needed.
What is the difference between roughing and backing?
Roughing is the initial pump-down from atmosphere; backing is keeping the high-vacuum pump’s exhaust pressure low during operation. The same pump often does both.
Written by the Girovac technical team. Girovac Ltd has supplied and serviced industrial and laboratory vacuum equipment from its North Walsham workshop since 1983. Last updated: July 2026.