Monitoring diaphragm and bladder accumulators with RFID
What is the quickest way to test the gas pressure in, for example, 400 hydro-pneumatic accumulators? The Werdohl fluid specialists from Stauff have found what is probably the most convincing solution to this challenge. The pressure is continuously recorded by sensors which are integrated into the connection adapter at the gas filler connection. They transfer the data to a reading device with RFID technology within a matter of seconds, wirelessly and without pressure loss.
Regular pressure testing on the gas side of hydro-pneumatic diaphragm or bladder accumulators is a standard maintenance task. This often involves different test intervals because the accumulators are sometimes integrated into safety-relevant hydraulic circuits or complex continuous production processes.
Companies who use a large number of bladder accumulators in production categorize these into different safety categories. Accumulators which are used in critical processes, such as for crane and other transport systems lifting extremely heavy loads, are tested at three-month intervals, for example, while others are checked every nine months and most only every 15 months.
Until recently, such a test meant that an appropriately trained maintenance engineer had to connect a pressure gauge or a gas cylinder with pressure gauge to the gas filler connection of the accumulator and test the pressure. This required opening the system, which can result in pressure loss.
To reduce this effort, a completely new solution is available for monitoring accumulator pressure – the accumulator adapters type SBAA and SDAA from the German fluid technology specialist Stauff. The interaction with the innovative pressure transmitters from the PT-RF range and a suitable reading device allows contactless monitoring of the pressure in hydro-pneumatic diaphragm and bladder accumulators – fast, easy and without any pressure loss.
The accumulator adapter is screwed onto the gas filler connection on the hydro-pneumatic accumulators and a pressure transmitter is permanently attached at the side. Existing systems can also be retrofitted with ease. The standard filling valve used on the accumulator is still used at the top connection of the connection adapter. Existing filling equipment can still be used as usual without any restrictions.
Depending on the requirements, PT-RF series pressure transmitters are capable of recording measuring ranges of between 0 - 16 bar and 0 - 600 bar (relative), which are commonly found in hydraulics, with excellent precision of max. ±0.5% based on the respective full scale. The functional principle of the sensors is based on innovative RFID technology: The energy required for a measurement is transferred wirelessly to the pressure transmitter via the antenna of the associated reading and display device, so that the transmitter requires no internal or external power supply and no wiring whatsoever.
When the pressure transmitter is activated at the press of a button on the device, a current measured value is determined within only 0.5 seconds and then immediately transmitted back to the reading and display device, output on the illuminated display and stored for further evaluation. In addition to the pressure value itself, other relevant information is also transmitted as a standard, including date and time of the measurement and the unique serial number of the pressure transmitter. This enables the clear assignment of the measuring point – a basic prerequisite for end-to-end documentation of the test results. Over 15,000 of these measurement data sets can be stored in the integrated memory of the reader. The software included in the scope of delivery allows subsequent evaluation and further processing of the measured results previously transmitted to the PC or laptop via the USB interface.
It is easy to see how the new technology now also brings benefits for system operators, maintenance personnel and service engineers when it comes to monitoring hydro-pneumatic accumulators: Measurements can be carried out very easily, without extensive training and within a few seconds at the press of a button, and then documented in a reliable process. There is no need to unscrew and re-install pressure gauges or other measuring and display devices – effectively a temporary opening of the system which can lead to the loss of accumulator pressure and result in impaired performance.
The following example illustrates the substantial savings potential thanks to fast and easy handling. Based on the required time before/without pressure sensors and after/with pressure sensors and 400 pressure accumulators, approx. 548 pressure tests are required per year due to different safety categories.
With the old method, this required 137 man hours per year (15 minutes multiplied by 548). This does not yet include processing of the data for documentation. Wireless polling of the PT-RF pressure transmitters, in the other hand, only takes the personnel 15 seconds per measuring point and requires no interfering with the gas supply. The actual measurement therefore only takes 100 minutes in total. And processing of the measurement results for documentation is also much simpler.