Fire sprinkler systems get safety torque

Sensor Technology Ltd: Replacing a torque meter with a torque sensor has revolutionised the validating process for bespoke Fireset sprinkler systems built by Grundfos Pumps Ltd. in Leighton Buzzard.

Grundfos designs and builds a vast range of electric and diesel driven Firesets that form the heart of any sprinkler system. These Firesets have sophisticated control systems that activate automatically when the presence of a fire is detected. They also have to meet the requirements of demanding Loss Prevention Certification Board to fire protection of building and their occupants.

Huw Lloyd, Engineering Manager for Grundfos Pumps Ltd. explains: “Even a moderate sized system can have many of the sprinklers heads. Typically just a few of these will go off to contain a small local fire, but the Fireset has to be able to deliver a predetermined pressure range to every head, even if they are all deployed.”

“It is important to make sure everything is correct before the Fireset leaves the factory, after all lives are at stake here.” So Grundfos subjects each Fireset to a rigorous performance test prior to despatch to prove that it does exactly what it is supposed to do.

The Fireset set is basically pump sized to comfortably meet maximum demand, either diesel or electrically driven. The control system is designed to automatically start the system up when a fire is detected and then to control the pressure of water needed to address the fire.

“We test about 100+ Firesets systems each year, which means the test area is in continuous use and we have to constantly look to improve our operating efficiency,” says Huw Lloyd.

“The critical part of the testing process is to confirm that the pumps performance is being achieved and to do this we need a torque meter that will withstand the tremendous amount of vibration present. We chose a torque meter that we were advised would withstand the vibrations of a tractor ploughing a field – but this wasn’t up to the job, so we asked sensor expert Morton Moeller of Sensor Technik to come up with a better idea.”

Moeller almost immediately recommended a TorqSense unit made by Sensor Technology not so far away in Bicester. TorqSense is superbly robust and has a first rate track record in arduous installations, and it had other attractions that put it head and shoulders above alternative sensors.

“The Grundfos specification was very wide, because their systems vary so much in size,” says Moeller. “I set myself the challenge of covering this with a single sensor so that Huw Lloyd and his team didn’t have to spend time swapping between big, medium and small units each test, and also to contain the procurement costs.”

Another great attraction is that TorqSense does not have to be physically connected to the Fireset under test by slip rings etc. Instead it monitors the torque via radio waves.

A shaft deforms very slightly when it rotes, the amount of deformation being proportional to the torque. TorqSense measure the deformation so that it can calculate torque. To do this two tiny piezo electric combs are glued to the surface of the shaft at right angles to one another; shaft deformation will expand one comb and compress the other. The radio frequency signal emitted by the TorqSense is reflected back by the combs, with its frequency changed in proportion to the combs’ deformation.

“The procedure to set up the TorqSense for each new test is to point it at the Fireset,” say Moeller. “The old system took a several hours of concentrated effort by a couple of Grundfos test engineers, and it needed an awful lot of resetting during the test. These savings alone represent a significant efficiency gain for Grundfos.”

Huw Lloyd is equally exuberant about the installations: “We’ve been using the TorqSense for the best part of two years now, so we’ve tested many different Firesets – big, small, simple and complex. The best thing I can say about it is that we had forgotten it was there; it does its job perfectly time after time.”