No trailer
6 minutes
For a vehicle to which the coupling of a trailer is not permitted, the time t2 to reach p2 must not exceed 6 minutes.
Source: UN Regulation No 13, Annex 7, Part A, 2.4.2.
Trucks, tractors and trailers brake with compressed air: UN Regulation No 13 sets how fast the compressor must fill the reservoirs and how many brake applications they must hold, and US rules set a compressor cut-in of at least 100 psi for trucks. Ultra Controlo distributes and services Thomas, which says its articulated piston compressors are most often used in medium and heavy duty air suspension systems.
UN Regulation No 13, the US standard FMVSS No. 121 and the US carrier safety rules in 49 CFR 393 describe these parts of the system.
Sized to raise the supply and service reservoirs from 85 to 100 psi, with the engine at its maximum recommended speed, within a time set by the reservoir capacity.
Service and supply reservoirs of at least 12 times the volume of the service brake chambers, each able to withstand five times the cut-out pressure or 500 psi, whichever is greater.
Each reservoir has a manually operable condensate drain valve; UN R13 asks for a draining and exhausting device in at least one reservoir of each service braking circuit.
A gauge in view of the driver shows service reservoir pressure; on trucks built since 1 March 1975 a warning comes on below 60 psi, and older power units warn at 55 psi or half the governor cut-out pressure, whichever is less.
After eight full-stroke applications of the towing vehicle's brake, the energy a trailer's reservoirs supply to its brakes must not fall below half the figure of the first application.
Sources: UN Regulation No 13 (OJ L 42, 18.2.2016, incorporating Supplement 13 to the 11 series of amendments), paragraphs 5.2.1 and 5.2.2 and Annex 7; 49 CFR 571.121 (FMVSS No. 121), 393.50 and 393.51 (eCFR, read 28 October 2026).
UN Regulation No 13, Annex 7, measures the time the compressor takes to raise the least-favoured reservoir from zero to p2, the pressure set by the vehicle manufacturer.
For a vehicle to which the coupling of a trailer is not permitted, the time t2 to reach p2 must not exceed 6 minutes.
Source: UN Regulation No 13, Annex 7, Part A, 2.4.2.
For a vehicle to which a trailer may be coupled, t2 must not exceed 9 minutes.
Source: UN Regulation No 13, Annex 7, Part A, 2.4.2.
After eight full-stroke actuations of the service brake control, the pressure left in the reservoirs must still give the prescribed secondary braking performance.
Source: UN Regulation No 13, Annex 7, Part A, 1.2.1.
In the US, FMVSS No. 121 instead sets the compressor capacity by the time to raise the reservoirs from 85 to 100 psi.
Thomas makes pumps and compressors for OEM equipment, and says its articulated piston compressors are most often used in medium and heavy duty air suspension systems. Ultra Controlo distributes and services the brand; its catalogue lists Thomas piston pumps for medical, automotive and industrial applications.
Oil-less piston pumps; Thomas lists vehicles, where they supply pressure and vacuum for air-operated suspensions, seats, clutches and doors.
ThomasOil-less, to 12 bar; Thomas says articulated piston compressors are most often used in medium and heavy duty air suspension systems, and lists central tyre inflation among their possible applications.
ThomasSources: Ultra Controlo Industrial 2026 catalogue, p. 15; Thomas, piston pumps technology and TASKAIR OIL-LESS Series pages (thomaspumps.com).
Ultra Controlo is a Portuguese manufacturer of compressed air, vacuum and technical gas systems, with 40 years of experience. We design, assemble and test our own compressors, dryers and carbon towers in Portugal, and supply and service five partner brands.
ULTRASCREW compressors, ULTRASEC and ULTRADRY dryers and ULTRAK activated carbon towers.
Gardner Denver, Elmo Rietschle, Thomas, Speck Pumpen (Circutec) and Speck Triplex.
Preventive and corrective maintenance, original spare parts and emergency support, by our own team.
Source: Ultra Controlo Industrial 2026 catalogue, pp. 3, 10, 16, 17 and 22.
UN Regulation No 13, Annex 7, says the time to reach the manufacturer's pressure p2 in the least-favoured reservoir must not exceed 6 minutes, or 9 minutes for vehicles to which a trailer may be coupled.
FMVSS No. 121 (49 CFR 571.121) says the air compressor governor cut-in pressure for each truck must be 100 psi or greater, and for each bus 85 psi or greater.
49 CFR 393.51 says trucks, truck tractors and buses built on or after 1 March 1975 must have the FMVSS No. 121 warning, which comes on when service reservoir pressure is below 60 psi. Older power units need a warning at 55 psi (379 kPa) and below, or half the governor cut-out pressure, whichever is less.
Yes. 49 CFR 393.50 says each reservoir must have a condensate drain valve that can be operated manually; automatic drains may be used if they can also be operated manually or a manual means of draining is kept.
Ultra Controlo distributes and services Thomas. Thomas says its articulated piston compressors are most often used in medium and heavy duty air suspension systems, and lists central tyre inflation among possible applications of its TASKAIR series.
Air suspension, tyre inflation or another air-operated system: the pressure, the air demand and the duty. We reply with the Thomas compressor or pump that fits.
