The Main Uses of Solenoid Valves and the Industries that Use Them

What Solenoid Valves Do

Solenoid valves are an advantageous solution for controlling the flow of many liquids and gases of a huge temperature range where either an “on” or “off” state is needed.  A piston that may contain a metal or soft disk either covers or moves away from an internal orifice separating the inlet from outlet.  When the piston is blocking the orifice, a pressurized fluid is held stationary at the inlet and up into the bonnet tube.  A differential pressure exists over the orifice area, for which the resultant force combines with any downward spring force to create a tight seal.  Upon energization of a solenoid, internal components move in various ways that result in the piston either moving away from or towards that orifice to open or close the valve.  If the valve was a “proportional” solenoid valve, essentially infinite positions of that piston could be created by varying the supply voltage to create a throttling effect. oriffice

Simple Setup

Solenoid valves are easy to install.  Many simply have two lead wires connected to a coil nested around a bonnet tube containing materials that easily magnetize and demagnetize.  Either wire can be line voltage.  Switches or relays can be designed into the control system to route power when needed to quickly open or close the solenoid valves.  Selection of a solenoid valve can eliminate the need for long and expensive air lines and air delivery systems that would be needed for pneumatically actuated valves.  For long wire runs on remote locations, higher AC voltages may be utilized to minimize power loss.  For example, 240V AC is commonly sold.

Voltages

Solenoid coils are offered in many voltages, typically 12, 24, 120, 240V DC, and 24, 120, and 240V AC, which suit the majority of applications. Coils are easily developed for less common voltages as well. While the valve may be designed to achieve catalog pressures assuming the nominal voltage, the valve may still operate effectively at voltages lower than those nominal values.  This feature is ideal for battery powered systems that may provide lower voltage over time.  An AC coil will generally run hotter than a DC coil wound for the same power output due to hysteresis characteristics of the magnetic circuit.  An AC coil will also have an initially high “inrush” of current on the order of 2-10 times the nominal steady state current.  A system designer should be aware of inrush amperage and heat outputs, along with the resulting coil surface temperatures.  These temperatures are dependent upon the duty cycle of the valve, which includes energization frequency and the duration held energized, along with ambient and fluid temperatures.  While it may take several hours for a coil to reach steady state surface temperatures, the majority of the temperature rise would be noticeable in the first hour.

Hazardous Locations and Explosive Atmospheres

Solenoid valves can be configured with certified explosion proof coils per UL-1203, CSA C22.2#30, and ATEX.  The copper coil wire may be encapsulated and isolated from any flammable gases that may be continuously present outside of the valve.  Flame proof designs consist of somewhat of a labyrinth so that even if flammable gas was ignited inside the coil, it would not propagate and ignite gas surrounding the valve.  For situations where flammable gases may be continuously present, electric motors are often not permitted due to sparking.  Taking this a step further, “intrinsically” safe coils with power outputs so low that they cannot ignite a gas may also be selected as well.  These, however, have very limited opening force due to such low power.  Industries concerned with flame propagation typically deal with natural gas processing and transportation, hydrogen refueling and fuel cells, methane recovery, and oil and gas in general.

Speed

Time to open and close is extremely fast on solenoid valves, and is often on the order of 50-300 milliseconds.  The smaller the valve, the quicker the small internal components can be made to move over short distances.  On piloted valves with larger traveling distances, viscous liquids tend the have the effect of slowing the movements down as internal components must push through those fluids.  Applications requiring a fast response time need look no further than solenoid valves.

Packless

Motor controlled valves and ball valves often have a stem that punctures the pressure boundary of the valve.  This stem is surrounded by a tight packing, often PTFE or graphite, to seal the high pressure fluid.  The packing may wear over time, and such wear may be exacerbated by shifting temperatures and ingress of contaminants.  Solenoid valves often have one motionless seam where the bonnet attaches to the valve body.  A gasket or o-ring of a material compatible with the working fluid can reliably be selected for this seam.  Radioactive applications sometimes do not allow the use of elastomeric gasket materials, so bonnets are welded to valve bodies.  Industries focused on minimizing fugitive emissions to reduce air pollution may opt for a packless solenoid valve.

Choosing Hydrogen Gas Valves

The Clark Cooper “EH” Series solenoid valves are frequently selected for hydrogen applications, which demand careful selection of materials to avoid a form of stress corrosion cracking known as hydrogen embrittlement.  Austenitic (304 & 316) stainless steels are the go-to for high pressure hydrogen containing components per Process Piping specification ASME B31.12, but the use of 430 stainless is unavoidable where magnetic pull force is needed.  Clark Cooper engineers have tackled the hydrogen embrittlement issue via several successful industry accepted approaches.  The bulk of the optimized weld seam is kept away from free floating hydrogen molecules.  The tight seam, which is essentially a fused area of 430 and 316 stainless, prevents hydrogen from working into the critical weld area.  The 430 stainless that is exposed is designed excessively thick and is not work hardened.  No quenched and tempered or precipitation hardened steels are used.  Strain hardening of the 316 tubing is kept below 145,000 psi ultimate tensile strength.

Clark Cooper ‘EH’ Series valves are designed to safely operate at up to 10,000 psig inlet pressures, and our ‘EX’ Series for 15,000 psi.  Strengths are validated by way burst testing, and our valves achieve burst strengths of around four times the maximum allowable catalog pressures, so buyers can be assured of safety.

With clean gases, Clark Cooper solenoid valves will achieve bubble tight sealing.  Seat and piston geometry optimization by our engineers, along with return springs to supplement contact force at low differential pressures, allows the valves to achieve this.

Surface temperatures of solenoid coils on Clark Cooper valves will stay well below what are already conservative temperatures for hydrogen applications, even in elevated surround air temperatures.  Generally speaking, the NEC 500 CEC temperature code is in the realm of “T3A”.  Coils are available with UL-1203, CSA C22.2#30, and ATEX certification.  Usage includes Class 1, Division, Groups A, B (hydrogen), C, and D gases.  The goal here is to guarantee that exposed hot areas of the coil never come even close to the ignition temperature of flammable gases that may be present.  Furthermore, areas inside the coil that may get significantly hotter are isolated and will never come in contact with surrounding gases.

Clark Cooper high pressure solenoid valves are fast as well.  The EH30 valve will open and close in less than 150 milliseconds, as indicated via pressure response readings at the connections.  The EH40 valves, with components that must move a little farther, can be expected to open and close in less than 300 milliseconds for gases.

Industry accepted “Cv” constants for our “EH” Series valves range from 0.005 on our smallest EH30 to 48 on the 2” EH70.  We can meet your flow rate requirements, and can customize when appropriate.  Various connection types are offered, and include NPT, SAE J1926, and the medium pressure metal to metal cone type, which we’ve found to be very appropriate for hydrogen.