So, you fitted a new tank. Great! How are you going to assess the amount of contents in your tank? It’s not a trick question, but many find that it’s harder than they expected to arrive at an answer.
Measuring the amount of liquid that goes into your tank, or that comes out of it, is easy enough. You just need a flow meter. But measuring the contents of a tank is a trickier business.
The first consideration in any tankage situation is safety. If you’re dealing with flammable or noxious materials, you may need to exclude some of the solutions below. Perhaps there’s a chance that a particular type of electronic sensor will spark and ignite fuel vapours. Or maybe the aperture required for a mechanical gauge will become a weak point, creating the risk of a chemical leak. Fortunately, manufacturers’ specifications are very detailed, and we can help to advise you on the suitability of your preferred solution.
You also need to consider accuracy. Exactly how accurate do you need your measurement to be? Some time-honoured solutions have margins of error as high as two per cent. That figure may sound trivial, but it becomes highly significant when you’re managing a 30,000-litre tank.
Tank Gauge Types
Sight Gauge / Level Gauge
Sight gauges (level gauges) are the most familiar measurement system — indeed, you may have one on your electric kettle! The gauge is simply a vertical tube of the same height as the main tank, allowing fluid to enter and fill it to the same level as the main tank. Sight gauges are simple and reliable, but they probably aren’t the best solution if you need a precise measurement… and they require holes in your tanks! If you want a sight gauge, it’s probably best to get it installed at time of purchase.
A float gauge (aka ‘cat-and-mouse’ gauge) is a little more sophisticated than a sight gauge. A float inside the tank attaches via a pulley mechanism to a marker mounted outside it. The float moves up and down as the tanks fills and empties, creating corresponding movements in the marker. Although the calibrated readout may suggest precision, float gauges are notoriously inaccurate. However, they do have an advantage over sight gauges in that the aperture is at the very top of the tank — so they’re a better choice where leakage risk is higher.
Hydrostatic gauges are taken to be a ‘step up’ from float gauges in terms of accuracy. A sensor mounted in the bottom of the tank measures the pressure exerted by the liquid, and a connected gauge — either analogue or digital — then converts that reading into a volume measurement.
Analogue hydrostatic gauges rely on a length of pressure tubing which links the sensor to a dial mounted on the outside the tank. In most cases they need to be pumped with a plunger in order to obtain a reading. (It’s a little like the way your GP takes your blood pressure.) Calibrating such a device can be quite a challenge, especially on horizontal tanks.
Digital hydrostatic gauges connect sensor to dial either via a slender cable or a wireless link. (When dealing with flammable substances, a wireless solution may be preferable because it eliminates the risk of electrical sparks.) Digital metering is more flexible than analogue, making it easier to calibrate to an unusual size of tank or a particularly dense liquid. It’s also relatively easy to fit a digital hydrostatic meter into an existing tank — indeed, the installation may not require any drilling.
However, the accuracy of hydrostatic metering can be compromised in cases where the liquid being stored is prone to separation and ‘layering’, or is sufficiently volatile to produce high gas pressures in the tank. Additional temperature sensing may be required to ensure accuracy in such cases.
Ultrasonic and Radar Gauges
Ultrasonic and radar gauges are generally taken to be the most accurate solutions available. They use sonar or radar techniques to ‘map’ the position of fluid in the tank. A smart digital meter then converts this information into a volume readout. Sensor installation generally requires a single, small drilling, but calibration is a job for a specialist.
Ultrasonic, radar and digital hydrostatic solutions are alike in that the use of wireless technology supports remote metering. It’s common to set up a monitoring station hundreds of metres from the tank, providing improved safety and convenience. Such systems may incorporate alarms and automatic temperature and pressure management solutions.
To find out more about our range of poly tanks, get in touch with one of our expert team on 01264 243116.