Technical Overview: Velvetrol® Technology in Gould Solenoid Valves

Introduction

The Velvetrol® feature represents a cornerstone technology that distinguishes Gould solenoid valves in industrial fluid control applications. As a standard component on virtually all Gould valve models, this internal piston pilot operated design delivers critical performance advantages that directly address common operational challenges in process systems, particularly the damaging phenomenon of water hammer.

Understanding the Velvetrol® Operating Principle

The Velvetrol® system employs an internal piston pilot operated mechanism that executes valve actuation through a precise two-step process. When the solenoid coil is energized, the pilot lifts off the piston, exposing a main orifice located in the center of the piston. Subsequently, fluid pressure above the piston releases through this main orifice, allowing inlet pressure combined with piston ring forces to open the valve. This entire sequence occurs in milliseconds, yet the design inherently moderates the closing action to prevent hydraulic shock.

The system requires a minimum pressure differential of 5 PSI across the valve for proper operation, leveraging line pressure to assist valve actuation rather than relying solely on electromagnetic force. This pilot-operated approach enables the valve to control substantially larger flows with minimal electrical input compared to direct-acting designs.

Combating Water Hammer: The Primary Design Objective

Water hammer – the pressure surge resulting from sudden flow stoppage or direction change – poses one of the most destructive forces in piping systems. Conventional solenoid valves, particularly in larger sizes, can close rapidly enough to generate shock waves exceeding 6,600 PSI, potentially damaging pipes, fittings, and equipment.

The Velvetrol® feature addresses this critical issue through its controlled closing mechanism. The internal piston design inherently follows a fundamental operating principle: the faster a valve opens, the slower it will close. This inverse relationship provides natural mitigation against hydraulic shock without requiring external devices. The pilot-operated configuration allows fluid pressure to gradually dissipate from the piston chamber, decelerating the closure rate and preventing the abrupt stoppage that generates water hammer.

For applications requiring additional protection, Gould offers optional slow-close configurations (designated as -81) that further reduce water hammer effects through factory-calibrated damping. This enhanced protection proves especially valuable in systems handling large volumes or operating at elevated pressures where hydraulic shock poses greater risk.

Packless Design: Eliminating a Maintenance Liability

Unlike traditional packed valves that rely on compression packing around the stem to prevent leakage, the Velvetrol® employs a packless construction. This design eliminates the stem packing gland entirely, offering several significant operational advantages:

Zero Fugitive Emissions from Packing: With no packing material to wear, compress, or leak, the packless design inherently prevents atmospheric emissions that plague traditional valve stems. This feature proves particularly valuable in applications involving hazardous, toxic, or volatile media where environmental compliance and worker safety are paramount.

Reduced Maintenance Requirements: Conventional valve packing requires periodic adjustment and eventual replacement as it wears and loses sealing capability. The Velvetrol® packless design eliminates this maintenance task entirely, reducing labor costs and minimizing downtime for packing-related service.

Consistent Performance Over Service Life: Packing material degrades over time due to thermal cycling, chemical exposure, and mechanical wear, leading to progressively deteriorating seal performance. The packless Velvetrol® design maintains consistent sealing throughout its operational life without the gradual degradation characteristic of packed valves.

Metal-to-Metal Atmospheric Sealing: The internal piston design achieves isolation through precision-machined metal surfaces and engineered elastomer seals (PTFE piston rings with stainless steel expanders), providing reliable containment without reliance on compression packing.

Full Port Construction: Maximizing Flow Efficiency

Our Velvetrol®-equipped valves features full port construction. This design philosophy delivers multiple performance benefits that impact both operational efficiency and long-term reliability:

Minimal Pressure Drop: Full port design reduces flow restriction to negligible levels, typically maintaining pressure drops substantially lower than reduced port alternatives. In extended piping systems, this pressure preservation translates directly to energy savings and improved system efficiency.

Maximum Flow Capacity: By eliminating the constriction present in standard port valves, full port Velvetrol® valves deliver flow rates matching the connected piping capacity. A 2-inch full port valve, for example, can handle approximately 200 GPM compared to roughly 150 GPM for a standard port equivalent—a 33% capacity advantage.

Reduced Turbulence and Erosion: The unrestricted flow path minimizes turbulence, which reduces erosive wear on internal components. This benefit extends valve service life and maintains performance consistency over time, particularly in applications involving abrasive media or high-velocity flow.

Pilot-Operated Efficiency Advantages

The pilot-operated configuration inherent to Velvetrol® technology provides operational benefits beyond water hammer mitigation:

Lower Power Consumption: Only the small pilot mechanism requires electromagnetic actuation, while line pressure performs the primary work of opening and closing the main valve. This results in substantially lower coil power requirements compared to direct-acting designs requiring higher wattage for equivalent flow capacity.

Superior Performance with Large Orifices: Pilot operation enables effective control of large valve sizes (up to 2" NPT with our stainless steel valves, 3" with our bronze line) without proportionally increasing coil size or power consumption. Direct-acting valves become impractical in larger sizes due to the electromagnetic force required to move large closure members against line pressure.

Extended Coil Life: Lower operating temperatures resulting from reduced power consumption extend coil service life. The Class F and H coils used in Gould valves feature waterproof, fungus proof molded polyester construction rated for continuous duty, further enhancing reliability.

Versatility Across Pressure Ranges: Pilot operation enables functionality across wide pressure ranges (5-1200 PSI depending on model) since system pressure assists rather than opposes valve operation.

Material and Construction Excellence

Velvetrol® equipped valves incorporate premium materials engineered for demanding service conditions:

Bodies: Investment cast CF8M (316) stainless steel for corrosion resistance and structural integrity, or bronze for standard service
Piston assemblies: 303 or 316 stainless steel with glass and molybdenum-filled PTFE piston rings
Springs and expanders: 316 stainless steel (KX series) for corrosion resistance
Pilot assemblies: 430FR stainless steel armature with 316 stainless steel pilot points
Seal options: Multiple elastomer and PTFE choices (Buna, Viton, PTFE, Ethylene Propylene) for chemical compatibility

This materials selection provides temperature capability from -40°F to 450°F and chemical compatibility with a broad range of media including water, air, inert gases, steam, oil, and many corrosive fluids.

Application Versatility

The combination of water hammer protection, packless design, full port construction, and pilot operation makes Velvetrol®-equipped valves suitable for diverse applications:

High-flow water distribution and treatment systems
Steam service up to 200 PSI
Compressed air and inert gas systems
Oil transfer and lubrication circuits
Corrosive chemical handling (with appropriate material selection)
Cryogenic applications (down to -420°F with special construction)
Hazardous locations (with NEMA 7 explosion-proof enclosures)

Installation and Operating Considerations

For optimal Velvetrol® performance, proper installation practices should be observed:

Mount valves in horizontal lines with coils upright and on top
Install a 40-mesh strainer (not larger) upstream of the valve to prevent particulate damage to pilot mechanisms
Verify coil voltage matches power supply specifications
Ensure flow direction aligns with body arrow
Select valve pressure rating closest to actual operating pressure for optimal performance

Conclusion

The Velvetrol® feature represents integrated engineering that addresses multiple operational challenges through a single, elegant design solution. By combining internal piston pilot operation with packless construction and full port flow paths, Gould has created a valve platform that mitigates water hammer while delivering low maintenance requirements, maximum flow efficiency, and operational reliability. For process engineers specifying solenoid valves for critical applications, the Velvetrol® technology offers quantifiable advantages in system protection, operational efficiency, and lifecycle cost reduction.