VESDA VLF

Aspirating Detection for Small Spaces

Aspirating smoke detection has historically been specified for large or high value spaces, because the cost and design effort only made sense at scale. That left many small rooms that genuinely needed very early warning protected by a conventional detector on the ceiling.

The VLF exists for those rooms: a comms room, a small server room, a switchboard cupboard, a plant room, an archive store, a lift motor room. Each one is small, and in most cases it’s the room a business can’t afford to lose.

The detection principle is the same. Air is drawn continuously through sampling holes in a pipe network, filtered, and passed into a chamber where laser based light scattering detects very small amounts of smoke. A clean air barrier protects the optics. What changes is the scale, and with it the cost and the complexity.

Out of the Box

This is the practical difference between the VLF and the rest of the range.

The VLF can be installed and commissioned out of the box, without a special interface or software programming tools. Thresholds arrive pre set, and AutoLearn doesn’t change them while it’s learning, so protection is continuous from the moment it’s powered up. Pre engineered pipe network designs keep simple installations simple.

For a single small room, that removes much of the specialist commissioning effort. For advanced configuration, the VLF is still supported by VSC and ASPIRE, and it can be configured offline or online, so the capability is there when a project needs it.

The Smoke Dial

The display is a ring of LEDs that shows the smoke level, rather than a numeric readout.

That sounds cosmetic, but it isn’t. Someone walking past a comms room can see at a glance whether the detector is reading nothing, reading something, or approaching alarm. A numeric display needs someone to stop, read it and know what the number means. On equipment that’s checked in passing rather than watched continuously, a visual indication that works from a distance gets noticed.

Alongside it, the Instant Fault Finder is opened through the field service door. It turns the Smoke Dial into a fault indicator that identifies the specific fault condition, such as filter, aspirator, high or low flow, or field wiring. That information can be passed to the fire service company, so technicians arrive fully prepared, turning a fault call into a fix rather than a diagnosis followed by a second visit.

Ultrasonic Flow Sensing

The VLF was the first air sampling smoke detector to use ultrasonic flow sensing, and Xtralis’s patented system is still the approach it uses.

Airflow through the pipe network has to be monitored, because a blocked or broken pipe is a detector protecting nothing. Ultrasonic sensing gives a direct reading of the sampling pipe flow rate. It’s immune to air temperature and pressure changes, and unaffected by contamination.

Two Models

Coverage figures depend on local codes and standards. The EN 54-20 class achieved depends on the pipe design and hole count, rather than the detector alone, and is calculated in ASPIRE.

For the VLF-250, Class A is achieved with 12 holes at 0.12% obs/m, Class B with 12 holes at 0.35%, and Class C with 12 holes at 0.80%. For the VLF-500, Class A is achieved with 30 holes at 0.05% obs/m, Class B with 30 holes at 0.15%, and Class C with 30 holes at 0.32%.

Alarms, Outputs and Logging

Four alarm levels (Alert, Action, Fire 1 and Fire 2) can be set from 0.025% obs/m, with individual alarm delays of 0 to 60 seconds. Two sets of alarm thresholds can be switched by time or through the general purpose input, which suits rooms with different day and night conditions.

Three changeover relays cover Fire 1, Action and Fault. The general purpose input can reset, disable or put the detector on standby, switch threshold sets, or act as an external input. Optional interface cards add VESDAnet or multifunction control.

Up to 18,000 events are stored, time and date stamped, in separate logs for smoke level, flow level, detector status and faults.

Where It’s Used

Communications and server rooms. Switchboard and electrical cupboards. Small plant rooms. Lift motor rooms. Archive and record stores. Small laboratories. Retail back of house. Hotel and residential plant spaces. Control rooms. Small cold stores. Museum and gallery display cases and stores. Any small room where losing the contents or the function would stop the business.