ABSTRACT

This paper presents a summary of experience gained in the design and application of hydraulic control valves in systems for subsea completions Salient requirements and design parameters for this specialized application are identified and practical difficulties arising from the use of control valves in a high reliability system are discussed. The effects of friction, interflow and pressure variations on both hydraulic piloted valves and electrical solenoid piloted valves are Included

INTRODUCTION

The high cost of lost production, high cost of retrieval of subsea components and the need for safe reliable operation have established the requirement for high quality control valves in subsea control systems This is equally true for piloted hydraulic, sequential piloted and multiplexed electro hydraulic systems. The main features requiring consideration when selecting or designing a control valve for long term subsea use are listed below

  • Hydraulic response time

  • Operating pressure

  • Latching or non latching

  • Type of hydraulic fluid

  • Interflow

  • Fluid Cleanliness

REQUIRED VALVE TYPES

The three basic types of control valves that have developed to meet the requirements for subsea control systems are.

  1. Hydraulically Piloted - The main fluid control ports are shifted open by a piston and returned closed by a spring The open piston is usually connected to a selector valve on the surface by a dedicated hose as shown in Figure 1 Figure 1 - TYPICAL CONTROL VALVE MAIN FLUID PORTING (Available in full paper)

  2. Sequential Hydraulically Piloted - The main fluid control ports are shifted open by a piston and returned closed by a spring or return piston from a reference supply The open piston is usually connected to a pressure sensitive pilot which is connected to the surface by a pilot hose Several pilots set for different trigger pressures can be connected to the same pilot hose thereby reducing the total number of hoses in a system This type of control valve has seen limited application when compared to the other types

  3. Solenoid Piloted - An electric solenoid operated pilot valve is used to shift the main control valve fluid ports open and a second solenoid pilot valve is used to shift them closed as shown in Figure 2 Figure 2 - DUAL PILOT CONTROL VALVES (Available in full paper)

These control valves are designed so that they remain in the last commanded position, thus the solenoid pilots do not require continuous power A variation is the electrically held fail safe control valve which has no latching feature This control valve requires continuous power on the solenoid pilot to apply pressure to the open pilot piston. The main seal slider is the same as the hydraulically piloted control valve shown in Figure 1. When power is removed from the solenoid, pressure is removed from the pilot piston and the control valve is closed by the spring.

HYDRAULIC RESPONSE TIME

Hydraulic response time can be separated into two main categories 1) charge time and discharge time of long hoses and

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