What inputs determine the size of a hospital medical vacuum plant?

Under the NHS England guidance HTM 02-01 (2026), a hospital medical vacuum plant is sized from the diversified design flow of the areas it serves, using a design flow per terminal unit and a diversity formula per department; the pumps should still supply that flow during maintenance on any pump plus a further single fault.

Does a day unit use the same demand basis as a 24-hour hospital?

No. HTM 02-01 (2026) says sites that are not open 24/7 should consider demand across their working hours only.

Is dental suction sized the same way?

No. HTM 02-01 bases dental high volume systems on 300 L/min at each chair cannula connector, with their own diversity rule.

How is a hospital medical vacuum plant sized?

Step 1: define the rooms

At design stage the project team defines the requirements of each room or space. HTM 02-01 (2026) notes that pipeline flow cannot be predicted precisely, so it gives guideline values that have proved adequate in practice. In general note II of its annex, Portugal's ACSS ET 03/2006 asks designers to confirm the number of outlets and the real utilisation coefficients, and to apply one of FD S 90-155, HTM 2022, AS 2896-1998 or SIS HB 370 when sizing the distribution; HTM 2022 has since been superseded by HTM 02-01 (2026), and section 16 of the same specification lists AS 2896-2011.

Step 2: apply design flows and diversity

HTM 02-01 gives, for each department, a design flow per terminal unit and a formula for the diversified flow Q. Medical vacuum is typically 40 L/min per terminal unit; each operating room needs 80 L/min because the surgical team and the anaesthetist may use suction together. In the formulas, n is the number of beds, treatment spaces or single rooms where the procedure is performed, not the number of terminal units.

Area (HTM 02-01, Table 10)	Design flow per terminal unit	Diversified flow Q
Emergency department, resuscitation room (per trolley space)	40 L/min	Q = 40 + [(n − 1)10]
Operating room	80 L/min per room (40 L/min per terminal unit)	Q = 80
Critical care areas	40 L/min	Q = 40 + [(n − 1)10]

For a 28-bed ward unit with single rooms, four-bed rooms and a treatment room, the diversified flow is based on 40 L/min. The pipework is then designed on the diversified flows and the permissible pressure loss.

Step 3: choose the pumps and the vessel

Capacity should match the calculated demand (10.5). Pump capacity is stated as free air aspirated in L/min, with the pump at 475 mmHg (63 kPa) and at 450 mmHg (60 kPa) at the plant pipeline connection (10.27).
The pumps are arranged so that, during maintenance on any pump and a further single fault, the remaining pumps still supply the system design flow (10.17). See how many pumps a plant needs.
The vessel is sized to minimise stop/start cycles, which should stay within the manufacturer's recommendation, typically six per hour (10.19), and the Table 20 note sizes the reservoir's water capacity at a minimum of the total design flow rate. ACSS sets a maximum of 20 starts per hour for each pump.

ULTRAVAC

ULTRAVAC plants are configured with 1 to 12 pumps of 3 to 1,600 m³/h each and vacuum vessels of 24 to 6,000 litres, so the number of pumps and the vessel size can follow the calculated design flow.