FAQ 1: Why do my Auto-Stop (Flo-Fuse) valves continue to leak in the closed position?

Many Marotta Flo-Fuses have a built-in automatic reset. This is simply a small orifice, always open, that bypasses the valve seat, allowing the gradual repressurization of the system downstream of the valve. When the pressure is equalized on both sides of the Flo-Fuse, the poppet return spring repositions the valve to the normally open position. A valve with this feature will always leak through the bypass bleed orifice when in the closed position; however, the valve is doing its job properly, shutting down a system when excess differential pressure across it indicates a problem downstream.

Flo-Fuses are available with a manual reset, which includes a needle valve to close the bypass orifice. These valves will not leak when closed, but will require someone to manually reset the Flo-Fuse. Manual reset is accomplished by opening the needle valve to repressurize the system downstream, allowing the spring-loaded main poppet of the Flo-Fuse to reopen.

For more information, this Flo-Fuse PDF file provides a thorough discussion of Flo-Fuse operation.

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FAQ 2: What is a Balanced Poppet Design, and what are the features and benefits of a balanced - solenoid valve?

In most cases it is beneficial to have a “balanced poppet” in a direct acting valve. Less force is needed to move the poppet because all forces on the poppet are nullified by equal and opposite forces. The solenoid coil has to counteract only the spring force. Marotta direct acting solenoid valves use a balanced poppet to keep solenoid coil size and power requirements to a minimum.

With a Balanced Design
D1 = D2 = D3 = D4

Features and Benefits of the Balanced Poppet, Direct Acting Solenoid Valve from Marotta Controls, Inc.

Reliability

• Simplicity of Design - The key to reliability has been achieved by adopting the direct action, balanced poppet concept

• Direct Action - Few moving parts… simple valve mechanism… fewer potential leakage paths.

• Balanced Poppet moving between two soft, bubble tight seats virtually eliminates pressure forces under all operating conditions.

• Soft Seats - positively retained – tightly seal gases or liquids. Patented retaining supports assure dimensional stability of the seats under severe pressure and temperature conditions.

• Short Stroke of the valve elements – inherent in balanced poppet design – permits use of energy efficient, reliable actuators. No need for large, high-powered solenoids.

• High Mechanical Efficiency of the valve mechanism (i.e. balanced poppet and soft seat) allows the use of small sealing and actuating forces.

• High Reserve Power Margin of solenoid. Short stroke combined with high mechanical efficiency provides a substantial reserve margin in a small, lightweight solenoid.

• Continuous Duty Solenoid has a high safety margin, exceeding class H1 insulation requirements. Coil winding is capable of withstanding temperature as high as 450o F.

• Environmental Extremes. For example, some models are operational even at 70 G’s and 2000 cps vibration, and 70 G’s shock.

• Qualified to exacting space age requirements. Valves of this design are qualified for and specified on many rocket, missile, flight and submarine applications. Proven in years of service; components manufactured in production quantities.

Versatility

• Pressure can be applied at any port or any combination of the three ports… flows in all the three directions can be controlled.

• Vacuum to 6000 PSI Operating Pressure- soft, yet positively retained seats, and the absence of net pressure forces on the poppet allow system pressures ranging from vacuum to 6000 psi.

• Wide Spectrum of Operating Fluids- with proper selection of commercially available materials for seats and seals, a great variety of gases or liquids can be handled. Valves with specially designed seals accommodate cryogenic, highly corrosive and exotic fluids.

• Large Selection of Optional Variations - valves of this design are particularly adaptable to accept optional equipment such as AC or DC solenoids, a variety of electrical connections, position indicators, and manual overrides. Valve bodies made of aluminum alloy, brass, or stainless steel with a selection of several port styles, are available.

• Fast Response - .010-.040 seconds depending on valve size, flow and current draw limitations. Controllable metering, required in some variable thrust nozzle applications, has been achieved with some models at up to 75 pulses per second.

• High Capacity for the given size. Balanced poppet principle permits use of relatively large valve seats resulting in high flow capacity of the units.

• Adaptability - Large selection of configurations (flange, plug-in or line ports) make these units ideally suited for all applications including breadboard arrangements or complex system packaging.

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FAQ 3: What are the advantages of using a valve manifold instead of individual valves?

Marotta manifolds provide improved performance, save space and decrease costs. No other method of system packaging can provide these advantages. The decision to use a manifold system or conventional component system requires careful consideration. Manifolds offer the following advantages:

ENGINEERING

• The customer can specify system performances and not component performances. Specifications can be stated simply, such as operational schematic arrangements and inlet and outlet requirements. The task of selecting the proper individual components is left to Marotta’s engineers.

• Manifolds permit early allocation of space, eliminating costly and time-consuming placement of individual components during design, drafting and fabrication.

PROCUREMENT

• Purchasing document preparation time is reduced with of a single document that covers multiple items.

QUALITY CONTROL

• Visual inspection, hydrostatic testing, radiography, ultrasonic testing, and inspection of joints are eliminated.

• Pre-testing of individual manifold components, then testing of the completed manifold prior to shipment provides increased confidence in the valve-system performance. Components can be removed for inspection or repair without shutting down the entire system.

MANUFACTURING

• Manifolds consolidate an array of components, piping and fittings into one neat, compact module – resulting in considerable savings of valuable space. Installation is quick and easy… just mount, connect the ports, and it is completely installed.

• Wrench clearance and removal access areas are easily defined and mock-up requirements are simplified.

• Costly tube bending, pipe cutting, brazing of joints and tightening of fittings are eliminated. On the average, manifolds eliminate 18 to 22 fabricated or welded joints.

OPERATION AND SERVICE

• Marotta manifolds guarantee a compatible system by using components which have been tested together and which are known to perform in harmony.

• Hand-operated controls are engineered and arranged to establish simpler operating procedures, thus reducing the chance of error.

• Reliability is increased by placement of the filter within inches of all manifold components.

Following the selection of the manifold function and type, the designer must consider the other system factors, i.e., system pressure, line media, flow, accuracy, or other terms of a critical nature, which would effect system performance.

Representative manifolds have met the requirements of environmental tests including MIL-S-901C and MIL-STD-167.

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FAQ 4: How does temperature affect solenoid operation?
 

Temperature and Solenoid Coils

1. Ambient Operating Temperature: -20°F to 160°F

• A 24 volt coil operating at 1 amp has a power rating of 24 watts.

• Heat rise of the coil is about 10°F per Watt.

• Temperature rise will be 10 • 24 = 240°F.

2. The maximum temperature rating for the insulation of the coil wire is 400 °F

• A combined ambient and heat-rise temperature greater than 400 °F may result in the breakdown of the coil wire insulation or cause the solder connections to melt.

3. Required information to specify a coil

• Ambient temperature of the system.

• Temperature of the line fluid.

• Amount of time the valve is energized.

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FAQ 5: What are some important solenoid valve terms?
 

Important Solenoid Valve Terms

• Pull-in Voltage: The minimum voltage required to actuate the valve at room temperature.
  

• Continuous Duty: The valve can be left energized indefinitely.
  

• Equivalent Sharp Edged Orifice Diameter (ESEOD): A way of sizing the valve. It equates the flow capability to an equivalent sharp edged orifice diameter.
  

• Valve Coefficient (Cv): Another way to size a valve. A valve with a Cv of 1 will pass 1 gpm at 1 psig.
  

• Line Fluid: Must be known for compatibility with o-rings, grease, internal materials in contact with line fluid.
  

Solenoid Actuator Components and Terminology

Solenoid Actuator Pull-in Voltage Test

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FAQ 6: What are the features and advantages of direct acting and pilot-operated solenoid valves?
 

Direct acting valve

On a Direct Acting Valve, the poppet blocks flow from the inlet port. This poppet is directly linked to the solenoid. When energized, the solenoid moves the poppet to either the open or closed position (as applicable), overcoming the force of the return spring (and pressure in case of an unbalanced design). When the solenoid is de-energized, the poppet return-spring forces the poppet back to its normal position.

NORMALLY CLOSED

De-energized Position

Flow from inlet to outlet port is blocked by the poppet. The poppet is tightly held against the seat by the poppet return spring.
 

NORMALLY OPEN

De-energized Position

Inlet port is open directly to outlet port.The poppet is held off the seat by the poppet return spring.
 

Energized Position

Inlet port is open directly to the outlet port. The solenoid holds the poppet off the seat against the force of the return spring.

Energized Position

Flow from inlet to outlet port is blocked by the poppet. The solenoid holds the poppet on the seat against the return spring force.

 
 
In most cases it is beneficial to have a “balanced poppet” in a direct acting valve. The main benefit is that less force is needed to move the poppet because all pressure forces on the poppet are nullified by the opposite forces under all operating conditions.

There are of course exceptions to the above statements. In some applications, it is beneficial to purposely create an “over-balanced” condition wherein the line pressure will either tend to force the poppet against the seat or force the poppet away from the seat. Two examples of this are:

• An over-balance that tends to force the poppet toward the seat may be used when leakage is the main concern.

• An over-balance that tends to force the poppet away from the seat may be used when opening response-time is the primary consideration.

Although this is a very simplistic explanation of Direct Acting Valves it will give a basis on which to compare to piloted designs.

PILOTED VALVES

In general, a Piloted Valve is one that uses pneumatic or hydraulic pressure to move the main poppet, and consists of two valves; the main valve and the direct acting pilot valve, which controls pilot (actuating) pressure. This pressure can be either internal line pressure or from an external source, thus describing the two types of piloted valves:

• Internally Piloted

• Externally Piloted

Internally Piloted Valves

The internally piloted design uses line pressure to move the main poppet. Inlet pressure is ported to the back of the poppet, assisting the spring in keeping the valve closed. When the pilot valve is actuated, pressure behind the poppet is vented, and the spring force is overcome by the inlet pressure, opening the valve.

The boost chamber pressure decreases, allowing the differential line pressure to open the main poppet. The line pressure forces the main poppet open because this poppet is not balanced and the unbalanced force is in the direction to open the valve.

The advantages of an internally piloted design over an externally piloted design

• ease of installation

• fewer leak paths

• pilot fluid is dumped downstream

Some disadvantages

• valve may open (or close) when outlet pressure exceeds inlet pressure (backpressure)

• slower response time and uncertainty of main poppet position without line pressure

Externally Piloted Valves

An externally piloted valve typically can use any source of constant pressure. The description of operation for an externally piloted design is similar to the internally piloted type.

The use of an external source for piloted pressure offers added flexibility and can diminish some of the drawbacks of piloted valves.

The advantages of an externally piloted design over an internally piloted design are

• position of main poppet can be maintained regardless of line pressure

• the effects of back-pressure can be minimized because pilot and line pressure are independent of each other and response times can be decreased by the use of high pilot pressure.

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FAQ 7: What are typical valves used in cold and warm gas propulsion systems?
 

Cold Gas Propulsion Systems

Warm Gas Propulsion Systems

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