FUNDAMENTALS Josh Cosford • Contributing Editor
Hydraulic symbology 302 – high response valves A “high response valve,” is a relatively new term used to describe valves whose performance is variable, dynamic and powerful. Previously only servovalves running technologies such as a torque motor could be classified as high response, but with the proliferation of contemporary electronics, feedback and programming, proportional valves have closed the gap. Now some proportional valves match the performance of servovalves, but for the purpose of this discussion, I’ll call them all proportional valves. I discussed proportional valve operators in Symbology 301 – Electrical and Electronic Symbols, which appeared in the August 2019 Fluid Power World magazine. However, only the electrical operators were discussed, leaving out any holistic explanation of a high response valve. In Symbology 302, I delve deeper to elucidate how electronic and hydraulic symbology intertwines to produce hybrid symbols reflecting the purpose of each valve. I should stipulate, electronic symbols in fluid power are not representative of electrical symbols, although anyone fluent in electronic symbology catches on quickly. As mentioned in earlier articles in this series, there exists not only the ISO 1219 standard for drawing fluid power (and electrical) symbols but also a less relevant ANSI standard for drawing symbols. However, this does not stop individual manufacturers from drawing and detailing symbols as they see fit, either for clarity or narcissism, depending on who you ask. I’ve chosen actual catalog symbols from major manufacturers, so their depictions stray from explanations outlined by me previously. Bonus points if you can figure out who is who. I’m starting with the symbols for proportional accessories valves – in this case, a proportional relief valve and a proportional flow control. I’ve sidestepped simple symbols because I know you’ve learned the basics by now, so you’ll see no bare-bones components made proportional by way of just a diagonal arrow. These are compound symbols using various individual symbols concomitantly performing a single hydraulic function.
Figure 1. Proportional accessories valves 26
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In Figure 1 the proportional relief valve sits nested in the dash-dot boundary line, itself illustrating the encompassing nature of this symbol. In this case, the valve is an ISO 4401 D03 subplate mounted unit, which although nothing about the symbol tells us this, the functioning P (Pressure) and T (Tank) ports are being used while the A and B work ports are simply blocked due to obsolescence. The bottom of this valve may or may not exist with O-ring grooves for the work ports, and the optioning of them depends on the functioning of the proportional valve, which could also be constructed as a work port relief valve. Both the P and T lines are shown with fixed orifices, a feature that protects the valve from saturation of flow. The valve is intended to operate in a pilot circuit, either by controlling system pilot pressure or as the singular control over a larger valve (like a slip-in cartridge element), so it flows very little. Pressure energy flows directly into the left of the relief valve, where the pilot line can act upon the currently offset arrow to move it into the open flow path should upstream pressure overcome the solenoid’s active pressure setting. You’ll notice this manufacturer uses no spring in the symbol of the valve, although I assure you the spring exists in the physical part. They have simplified the operator as a simple solenoid rectangle bisected with the diagonal variable arrow. The diagonal arrow will be common to most, if not all, proportional valves, showing us that the current can be varied to adjust the position of a valve spool or poppet to achieve various ends. The manufacturer embellishes the symbol with a 7-pin connector, which is a common connector used for proportional valves with onboard electronics. Those electronics will include an amplifier circuit to take the input power and control signal and turn it into a PWM output the valve can use. As discussed in the earlier article, the triangular amplifier symbol differs slightly in fluid power from electronic symbols by way of the dashed line, so as to not confuse it with a pneumatic pilot source. A final note on this symbol is that the manufacturer used the circular connection node at the pressure port of the relief valve, something not standard for an ISO symbol. The next symbol in Figure 1 is also that from a major manufacturer, and at first glance appears to have a lot going on. It looks primarily like a 2/2 directional valve, and essentially it is. I’ve colorized this one to make explanations easy, but please note my color choices do not reflect any standard. It starts with a 2-way, 2-position valve symbol which is normally closed in neutral, with both A and B work ports blocked. The highly experienced among you will have noticed the dark red pilot line starting at the A port and working around to the right side positional
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