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Operators & Valves Direct Acting Pilot Operated Valves Construction Glossary

Operators & Valves

Solenoid operators and valves are devices which control the flow of liquids, gases, steam and other media. When electrically
energized they either open, shut off or direct the flow of media.

Operation -
The solenoid consists of a coil of wire wound in the form of a cylinder around the bobbin. When an electrical current is introduced, it resembles a bar magnet. When energized by an electrical signal, a magnetic field builds up which attracts the movable plunger to the polepiece against the tension of the main plunger spring. When de-energized, the magnetic field dissipates and the plunger returns to its original position, under the action of the main plunger spring.

In order to be usable on AC current as well as DC, the polepiece contains a shading ring to average the alternating sine wave and minimize AC hum. (Note - It is not necessary to use a shading ring for DC applications as DC current does not produce an alternating wave function.) The flowing media is normally permitted to enter the area between the plunger and plunger guide tube, and caution should be used to assure that these components are compatible with the media when selecting a valve.

Construction -
There are two types of construction available; Direct-Acting and Internal Pilot Operated.

Direct Acting

Direct-Acting Operators and Valves -
With a direct-acting valve, the solenoid plunger directly opens or closes the orifice, and the sealing disc is attached to the plunger. In the case of a Normally Closed operator or valve, the orifice is closed when de-energized. In the energized condition, the orifice is open. The valve will operate from zero (0) psi (pounds per square inch) to its maximum rated pressure. In the case when the operator or valve is Normally Open, the orifice is open when de-energized. When energized, the orifice is closed. The valve begins at its maximum rated pressure and is operated to close flow or zero (0) psi.

Direct-Acting 2-Way valves are shut-off valves with one valve inlet and one valve outlet port.

Direct-Acting 3-Way valves -
Direct-Acting 3-Way valves have three port connections and two orifices. One orifice is always open and the other closed. When the valve is energized, the mode reverses, hence the description 2-Position. Figure 3 shows a 3-Way, 2-Position Normally Closed valve. With the coil de-energized, the plunger main spring tension holds the lower seating disc tightly against the lower orifice, and shuts off flow. Port A is exhausted through Port R. When the coil is energized, the plunger is pulled in and the orifice at Port R is sealed off by the spring loaded upper seat disc. The fluid media now flows from Port P to Port A.

Other Functions -
Various functions can be obtained according to where the fluid media is connected.

3-Way Diverting -
Pressure enters the valve through a common inlet Port A. The flow is diverted through the two outlets Port R and Port P by energizing or de-energizing the solenoid.

3-Way Mixing -
This valve allows the selection of two different pressures through two different inlets Port R and Port P by energizing and de-energizing the solenoid. The fluid media is then routed through a common outlet Port A.

Pilot Operated Valves

Internal Pilot Operated Valves -
This type of valve is provided with a 2-Way pilot solenoid operator. A diaphragm or piston provides the seal for the main seat. These valves are used for switching pressures in conjunction with orifice sizes larger than those available with direct-acting valves. The floating diaphragm construction requires a pressure drop across the main valve seat to remain in the open position, or a coupled diaphragm or piston which is mechanically held open by the solenoid plunger (i.e. Chem-o-sol). The coupled type will operate with zero pressure drop across the main valve seat.

An Internal Pilot Operated 2-Way valve is shown in Fig. 4. When the solenoid is energized, the plunger opens the pilot orifice and relieves pressure from the top of the diaphragm to the outlet side of the valve, through the pilot channel in the main body. This results in an unbalanced condition which causes the main line pressure to lift the diaphragm off the main seat, thereby opening the valve. When the solenoid is de-energized, the pilot orifice is closed and full line pressure is applied to the top of the diaphragm, through the bleed orifice located in the diaphragm, from the inlet side of the valve, thereby providing a seating force for tight shut-off. As long as a pressure differential exists between the inlet and outlet ports, a residual shut-off force is available by virtue of the larger effective area on the top side of the diaphragm. In certain cases an internally piloted valve will require a minimum line pressure to insure sealing of the main orifice. This is due to the fact that the diaphragm is usually produced in a flat fashion and is made of some type of elastomeric material which will have a tendency to pull the diaphragm back to its normal position.

External Pilot Operated Valves -
With these types of valves, an independent external pilot source is used for controlling the pressure for actuation purposes. These valves are either piston or diaphragm types and may be actuated by either air or liquids.

A 3-Way solenoid pilot valve controls the independent external pilot media. In the case of externally piloted valves, the standard internal pilot valves are manipulated in a manner which separates the main valve into two sections. The upper section is the pilot pressure chamber and the lower section is for main media control. In the normal position, with pilot pressure, the main valve is closed preventing the flow of media. Pilot pressure is interrupted when the solenoid is energized. The plunger is pulled from its normal position to the raised position, closing off the pilot inlet orifice. At the same time the pressure is released from the pilot chamber of the valve by means of an exhaust port. When the solenoid is de-energized, the plunger returns to its normal position closing the exhaust port and the pilot pressure again builds in the pilot chamber, creating the diaphragm closing force. Fig. 5. (Note - All externally piloted valves will fail to open if for some reason the pilot supply pressure is interrupted).

The Normally Open and closed functions of the main valve rely on the function of the pilot valve. For example, a Normally Closed external pilot valve requires a Normally Open pilot valve. Conversely, a Normally Open external pilot valve requires a Normally Closed pilot valve.


Component Construction -

Coils -
All Spartan Scientific solenoid valves contain a completely nylon encapsulated magnetic circuit. The bobbin windings have a class H insulation rating or 390°F. For the DIN spaded version, each connector tab is silver plated to assure excellent conductivity. Each coil is fastened to the plunger guide tube by means of a hold down nut for ease of change-over without interrupting the pneumatic circuit.

Armature Assembly -
The armature assemblies are constructed of metallic components designed to provide protection against incompatibilities of various fluid medias. However it is necessary to use caution when specifying a solenoid valve for an unfamiliar fluid. Use caution when selecting a material suited specifically for the media.

Valve Bodies -
It is suggested to use caution in selecting a body material for unfamiliar media.

Temperature Considerations -
Most Spartan Scientific valves are manufactured to operate with fluids at a maximum of +60°C (140°F), and an ambient temperature range of +10°C to +50°C. (+50°F to +122°F). Other temperature limits can be supplied upon request for special applications.

Response Times -
With Direct-Acting valves, the response time is measured from the moment of electrical energization to the point when a figure of 90% of the pressure rating is attained at the valve outlet. The small moving masses and relatively high magnetic forces involved means that rapid response times, mostly in the region of 10 to 20 milliseconds, are obtained. The response time for an internally piloted valve is determined by the size, design, operating function, fluid media, temperature, inlet pressure and pressure drop.

Pressure Range -
Spartan Scientific valves will work reliably within the pressure ranges as shown in the catalog. The data is valid for a voltage band from -10% to +10% of nominal rated voltage. When a 3-Way valve is used for a function other than that which it was supplied, the permissible pressure range is altered. DC voltage valves operate at a lower maximum pressure than AC counterparts. Pressure ranges listed in the catalog are for DC voltages.

Flow Rates -
The flow rate through a valve is basically determined by the nature of the design and flow path through the valve. The size of the valve required for a particular application is generally established by the Cv flow factor. The Cv Flow Coefficient is defined as "the number of gallons per minute of water that will pass through a given flow restriction with a pressure drop of 1 psi". In most cases, the size of a valve can be determined graphically given a few known factors: gallons per minute, cubic feet per minute, pressure drop, inlet pressure, outlet pressure & Cv coefficient.

Bubble-tight Sealing

Air leakage between the internal sealed ports of a valve in either the energized or de-energized position is undetectable in a 5 second soap bubble test.

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Continuous Duty

A rating given to a valve that can be energized continuously without overheating.

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Current Drain

The amount of current (expressed in amperes) that flows through the coil of a solenoid valve when it is energized.

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Cv Factor

The Cv factor of a valve is the quantity of 60°F water, expressed in gallons per minute, which will flow through a valve with a one psi pressure drop. Spartan Cv factors for solenoid valves are listed for each series in the catalog.

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The normal opening of a closed valve and then closing is one complete cycle.

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Cycle Rate

The number of times a valve can open and close in a given time frame.

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Dead-End Gas Service

A condition in which a valve is energized but has no cooling fluid flowing through it because of a dead-end line (a cylinder pressurized for a long period).

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See NEMA classifications.

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Duty Cycle

The longest time that a valve is energized, followed by the shortest time that it is de-energized.

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A soft synthetic rubber which is suitable for water above 180°F and steam under 50 psi. EPDM has a wide range of fluid compatibilities but cannot be used with petroleum based fluids or fluids so contaminated (such as lubricated air).

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Explosion-Proof Construction

A solenoid valve constructed to meet the specifications of Underwriter's Laboratories, Inc. for operation in hazardous locations. See NEMA classifications also.

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A soft fluorocarbon insert material, developed primarily for handling hydrocarbons and high temperatures. FKM®* is the standard seal material in most Spartan Scientific general purpose direct poppet 2-Way and directional 3-Way valves.

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Floating Bottom or Top Seal

A plunger assembly construction in 2-Way and 3-Way valves in which the seal is movable against a spring within the plunger.

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The movement of fluid created by a pressure differential.

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Flow Capacity

The amount of fluid a valve will pass under given temperature and pressure conditions in gallons per minute or cubic feet per minute as measured at the outlet port. Cv is a measure of flow capacity.

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The amount of fluid that passes a given point at a given period of time.

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Flux Plate

A magnetic steel plate used in the magnetic circuit of a solenoid valve to help carry magnetic flux from the enclosure to the sleeve assembly. A flux plate is required on valves with non-metallic body material.

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General Purpose Valve

Valves suitable for application indoors under normal atmospheric conditions. See NEMA classifications. Intermittent Duty Coil - A valve coil not designed for continuous duty but which will perform satisfactory for a specified duty cycle.

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Heat Rise

The difference between the stabilized temperature of the solenoid coil when energized and de-energized in a constant ambient temperature. As current flows through a coil, heat is generated. The coil temperature rises until the coil enclosure dissipates heat as fast as it is generated, and the temperature stays at a stabilized level.

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A material used in the plunger assembly to seal an orifice.

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Intermittent Duty Coil

A valve coil not designed for continuous duty but which will perform satisfactory for a specified duty cycle.

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combination of carbon and halogens which yields a colorless material that is exceptionally stable, temperature resistant, chemically inert, and a true thermo plastic. The Kel-F®** plastic is an extremely versatile material and is impervious to the action of corrosive chemicals and highly resistant to most organic solvents.

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Leakage, External

The leakage between the internal part of the valve and the external part of the valve. Spartan valves are bubbletight.

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Leakage, Internal

The leakage between the internal sealed ports of a valve in either the energized or de-energized position. Leakage rate is normally described in cc (cubic centimeters) per minute or as bubbletight.

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Manual Override

A mechanical device that permits manual opening of Normally Closed valves or closing of Normally Open valves.

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Maximum Operating Pressure Differential (MOPD)

The maximum difference in pounds per square inch between the pressure at an inlet port and the pressure at an outlet port at which a solenoid valve will operate.

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A mechanical device that permits manual adjustment of fluid flow through a valve. Speed control.

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Minimum Operating Pressure Differential

The minimum difference in pounds per square inch between the pressure at an inlet port and the pressure at an outlet port required for proper operation of the solenoid valve. The minimum operating pressure must be maintained throughout the operating cycle of pilot-operated valves to ensure proper shifting from the closed position to the open position or vice versa.

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A soft synthetic rubber which has excellent compatibility characteristics for most air, water and light oil applications up to the 180°F - 200°F range.

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NEMA CLASSIFICATIONS (Solenoid Enclosures)

Type 1: General Purpose - Enclosures are intended for indoor use, primarily to prevent accidental contact of personnel with the enclosed equipment in areas where unusual service conditions do not exist. Type 2: Drip-Proof - Enclosures are intended for indoor use to protect the enclosed equipment against falling non-corrosive liquids and falling dirt. Type 3R: Rainproof and Sleet Resistant (Ice Resistant) - Enclosures are intended for outdoor use to protect the enclosed equipment against rain, sleet and external ice formation. Type 4: Watertight and Dust-Tight - Enclosures are intended for indoor or outdoor use to protect the enclosed equipment against splashing water, seepage of water, falling or hose-directed water and severe external condensation. Type 4X: Watertight, Dust-Tight and Corrosion-Resistant - Enclosures have the same provisions as Type 4 enclosures and are corrosion-resistant. Type 6: Submersible - Enclosure protected against entry of water during occasional temporary submersion at a limited depth. Type 7: Explosion-Proof - Designed to be used in hazardous atmospheres classified as Class I, Groups A, B, C or D, as defined by NEC (National Electric Code). The explosion-proof enclosure must be able to withstand an internal explosion and prevent the ignition of atmospheric gases which may be caused by the shorts or sparks occurring within the enclosure. Additionally, the external enclosure temperature must be low enough as to not ignite a surrounding flammable atmosphere. Type 9: Class II, Division I, Group E, F or G - Enclosures are intended for indoor use in the atmospheres and locations as defined as Class II, Division I or Division II, and Group E, F or G in the NEC to prevent the entrance of explosive amounts of hazardous dust. If gaskets are used, they must be of non-combustible, non-deteriorating, vermin proof material. Type 12: Industrial Use - Dust-Tight and Drip-Tight - Enclosures are intended for indoor use to protect enclosed equipment against fibers, filings, lint, dust and dirt; and light splashing, seepage, dripping and external condensation of non-corrosive liquids.

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An opening or passageway for the inlet or outlet of a fluid in a valve. The terminus of the port is threaded (NPT) to accommodate a line connection. A port designated with an NPTF indicates dry seal threads.

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Port, Cylinder

A port which provides a passage to or from an actuator.

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Port, Exhaust

A port which provides a passage to the atmosphere.

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Port, In

A port which provides a passage from the source of fluid.

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Port, Normally Closed

A port that is closed to fluid flow when the valve is de-energized.

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Port, Normally Open

A port that is open to fluid flow when the valve is energized.

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Port, Out

A port where the fluid leaves a two-way valve.

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Power Consumption

The number of watts a solenoid valve draws when energized.

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Force per unit area. Pressure is induced into a system by means of a pump, compressor or by gravity. Pressure may be expressed as pounds per square inch absolute (PSIA) or as pounds per square inch gauge (PSIG). PSIG is most often used for valve ratings and is 14.7 psi greater than absolute pressure, when measured at sea level.

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Pressure, Burst

The maximum pressure that would not cause the weakest section of the valve to fail and cause external leakage when pressure is reduced back to rated pressure. Depends on the individual valve construction. For most valves it is at least 5 times rated pressure.

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Pressure, Differential (Drop)

The difference in pressure measured between two given points. (P1 - P2).

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Proof Pressure

The maximum pressure the valve may be exposed to without suffering any damage. It does not have to be capable of operating at this pressure. For most valves it is at least 1-1/2 times the rated pressure. (This is a non-destructive test).

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Response Time

The length of time required for an operating mechanism of a valve to move from the fully closed to the open position, or vice versa. Response time will vary according to pressure, fluid, voltage and system. It also varies with type of valve (direct operated or pilot operated). For specific valves, consult factory with complete application details.

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The term used to indicate that the valve has a plunger return spring. A spring-loaded plunger permits the valve to be mounted in any position without causing malfunction.

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A synthetic material used for many semi-corrosive and corrosive media. It is virtually indestructible by any fluid, and its temperature resistance makes it especially suitable for steam application. Teflon®* has excellent lubricating characteristics. It is not recommended for vacuum service.

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Temperature Range

Spartan Scientific valves are equipped with high quality coils suitable for continuous energization. The permissible coil temperature, as measured by the change in resistance method, is 155°C for Class F and 180°C for Class H.

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Vibration and Shock

Most valves will resist 10 G’s or more.

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