Low power pilot valves reduce cost, improve safety, extend life
Wim van de Haar, Marketing Manager at ASCO Numatics, takes a look at the latest technologies being applied to pilot valve design and development to meet customer's needs for low power solutions.
Solenoid valves have been used for more than 100 years in diverse flow control applications across many industries. As markets have emerged, manufacturers have developed new products and improved the performance of existing ranges to meet this growing demand. However, with installation and lifecycle costs taking a high profile, the focus for many end users has meant a move to lower power devices. Devices that use less power mean better economics and improved safety.
There are also emerging applications specifically for low power valves. For example, when these are combined with the latest wireless and solar technologies for automation or control they provide new opportunities in remote or hard to reach locations. The challenge for the manufacturer has been to reduce the power requirements of existing ranges and develop new technologies that provide high performance and reliability with minimum power consumption.
Installing low power valves provides many benefits. For example, lower power consumption means more devices can be connected directly to control devices such as Process Control Systems (BPCS) and PLCs. Power supplies can be reduced in capacity or quantity, providing savings in cost and space. If the system is critical it may need to be protected by an uninterruptible power supply (UPS) and again a lower capacity unit can be specified. Reduced current means less voltage drop in the cable and it is therefore possible to increase operating distances or specify smaller cabling, providing economies in cable management devices such as channels and trunking. The higher resistance to undervoltage drops improves safety and, although the savings are not claimed to be huge, users can also expect to see lower energy bills.
Apart from these obvious savings over the life of a product there are other benefits associated with low power valve technology. Reduced power consumption means less heat being generated as the losses in the magnetic system are reduced. Heat can be an issue in a sealed cabinet where a bank of conventional solenoids can quickly raise internal temperatures beyond the specifications of other electronic devices in the cabinet. Removing excess heat may require fans, air-conditioning, or other cooling apparatus adding expense and increasing running costs. Solenoid coil heat also reduces a valve's life expectancy. So what are the options for low power technologies?
Direct acting pilot valves: With direct acting valves, the magnetic force of the solenoid acts directly on the valve's operating mechanism. These valves do not require a minimum operating pressure which limits the pressure and flow capabilities of this group of valves. By optimising the magnetic circuit of the device using the latest materials and computer aided design techniques, power consumption can be significantly reduced without compromising the valve's performance.
A good example of a product that has been modified to meet the need for solenoid valves with lower power consumption is the ASCO 327 series of direct acting solenoid pilot valves. The ASCO engineers have reduced the power consumption of this range by using the most efficient solenoid, providing it with an enhanced magnetic circuit to further optimise its performance. The combined effect of these innovations is a reduction in power consumption from 11.2W for the standard product, to just 1.8W in the low power version. With a flow factor (Kv) of 0.45, this is the only true direct acting solenoid pilot valve in this flow size without booster electronics. Booster electronics can increase the risk of failure and also introduce a response time delay.
Pilot operated spool valves: A pilot-operated spool valve uses the inlet pressure to actuate the valve mechanism. Because pilot operated valves are indirectly controlling the flow, they generally have a lower power consumption. Because of this they require a minimum operating pressure differential to operate. The ASCO Numatics (WS)LPKF low power solenoid which is used on the ASCO Numatics 551-552-553 ranges of spool valves has a power consumption of just 0.5W at 24V DC - the lowest consumption of any Ex d certified solenoid valve for the process industry. These valves have a large flow range of up to 860 l/min for the 551 valve and 3800 l/min for the 553 valve. Certified according to ATEX, IECEx and FM, the valves are ideally suited to applications where high levels of safety and superior resistance to aggressive operating environments are required.
Flapper nozzle technology: Flapper nozzle technology provides an ultra low power consumption pilot that is designed to be mounted on pneumatic valves used in explosive atmospheres or in industries where harmful substances are present. Flapper technology controls the air supply to the main valve. Energising or de-energising the flapper moves it closer to or further away from the nozzle, changing the pressure in the spool and operating the valve. Energising a flapper requires very little energy, resulting in a pilot valve with ultra low power consumption.
As an example, the ASCO Numatics ultra low power pilot for Series 551 spool valves, which is based on this technology, has a power consumption of just 30mW. Flapper technology also means that the pilot can be used in Zone 1 areas (ATEX Directive) and provides a high operational life. The series 551 with its proven flapper-nozzle technology provides an operating life of up to 25M cycles (solenoid pilot).
Piezo technology: The piezoelectric technology can be used to provide a high technology solution where extremely low power consumption is required. The effect can be seen in certain crystalline minerals. When they are subjected to a mechanical force, the crystals become electrically polarised. The converse of this relationship is also true. When these voltage-generating crystals are exposed to an electric field they lengthen or shorten according to the polarity of the field, and in proportion to the strength of the field.
This effect is used in multi-layer piezoelectric elements which are the essential part of piezoelectric valves. The elements consist of at least two layers. When energised, one layer contracts and the other expands resulting in a bending effect, similar to that seen in thermo-bimetals. The bending effect is used to open and close the valve.
ASCO Numatics uses this effect in the PIEZOTRONIC valve with proportional control. This is a high-tech solution designed in particular for those applications that demand an extremely low power consumption. The multi-layer technology reduces the power consumption to just 0.003W and the control voltage to only 20 to 40 volts making these valves suitable for use with battery-operated equipment or in potentially explosive areas. A long service life of 1 billion cycles means it is also suitable for integration into measuring systems such as medical equipment and gas analysers.
In conclusion, we can see that eliminating unnecessary power consumption saves money by reducing the size of copper wiring and the associated cable management devices, and by allowing the capacity and physical size of power components to be optimised. Lower power consumption means less heat is generated reducing the need for ventilation or forced cooling by fans. This reduces costs and simplifies the installation. In addition, by running components at a reduced temperature their operating life is extended lowering failure rates and reducing maintenance costs. Using lower power devices will reduce energy usage resulting in lower energy bills and a reduction in CO2 emissions.
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