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Pressure Sustaining Normally Open (PSNO) Valves

Pressure Sustaining Normally Open (PSNO) Valves are the universal solution for all types of filters to maximize flush cycle efficientcy. A PSNO valve will ensure that the filter initiates a backflush cycle with the required pressure by maintaining the correct pressure upstream of the valve (downstream of the filter). Filters flush more efficiently resulting in less maintenance, less downtime and less water and energy used. There is no need for a larger pump, saving capital and operating expenses, to achieve the correct pressure during backflush for proper cleaning.

Product Advantages

  • Accurate stable control of the upstream pressure is maintained by the PSNO Valve pilot even with changes in flow
  • Quick reaction time is acheived since the PSNO Valve goes into sustaining mode right before filter starts flushing
  • Easy installation and operation along with reliability resulting in less maintenance
  • Hydraulic valve with direct sealing diaphragm – no stem, shaft or bearings within the water passage for longer life

Applications

  • When valve upstream pressure is not enough for proper filter flushing
  • Ideal for all types of filters – media or disc

Pressure Sustaining Normally Open (PSNO) Valves Operation

A PSNO Valve is always installed downstream of the filter. During standard operation, filtration mode, the PSNO Valve is fully open and flow or pressure to the field is not restricted. The solenoid is not energized at this time (See Figure 1).

During the flushing mode, the solenoid is energized and the PSNO Valve partially closes in order to provide the desired pressure to the filter for proper flushing. This is referred to as the sustaining mode. During the sustaining mode, the valve maintains a “set” upstream pressure regardless of flow rate or pressure variations (See Figure 2).

At the end of the flush cycle, the solenoid is de-energized and the PSNO Valve will fully open again.

Figure 1: PSNO Valve Filtration Mode – valve is fully open and upstream pressure is 30 psi.

Figure 2: PSNO Valve Flushing Mode – valve partially closes and upstream pressure raises to 40 psi (or any other adjustab;e set point).

4″ PSNO PVC Valve

Pressure Sustaining Normally Open (PSNO) Valves Technical

Pressure Sustaining Normally Open (PSNO) Valves ship pre-assembled by Netafim USA following strict quality standards. The PSNO Valve consists of a Basic Valve, a Normally Closed Solenoid, a Pressure Sustaining Pilot, and an Accelerator Relay (if the valve is 6” and larger).

  1. Basic Valve – A basic valve consists of four simple parts – body, spring, diaphragm and bonnet – making it the simplest valve to operate and maintain. Installation is quick and easy with its unique inline design which also creates low losses at high flow rates. Available in two body material options – PVC or Iron – both with a direct sealing natural rubber diaphragm.
  2. Normally Closed Solenoid – A solenoid valve receives an electric command from a controller and converts it into a hydraulic command to the main valve. This enables the opening and closing of the valve by allowing the passage of water into or from the control chamber of the main valve. PSNO valves are standard with a 24VAC Normally Closed solenoid.
  3. Pressure Sustaining Pilot – A pilot is a mini-valve which ensures accuracy of the regulated pressure for hydraulic control valves. In PSNO valves, when the line presure is lower than the pilot’s spring setting (the set point), the pilot permits the passage of water into the chamber of the main valve, partially closing the vlave. PSNO valves are standard with a Green Pilot Spring and a recommended set point of 45 psi.
  4. Accelerater Relay – An accelerateor relay is designed with a large flow of passages to allow faster reaction time of the main PSNO valve. As soon as the solenoid is energized, the relay allows larger amounts of water to flow into the main valve chamber, partially closing the valve. It is a standard component on all 6″ and larger valves.

Pressure Sustaining Normally Open (PSNO) Valves Ordering Information

Selection Guidelines

When selecting a PSNO Valve, the following recommended flow ranges should be considered to ensure proper sizing and performance.

It is recommended not to oversize the PSNO Valve. In relation to the specfic flow (GPM), an oversized valve will require the diaphragm to be almost closed in the sustaining mode which can create high velocity, unstable regulation and potential cavitation.

Ordering Example

Pipeline: 6”

Required Flow Rate: 500 GPM

With a flow rate higher than 400 GPM, but lower than 600 GPM, a 4” valve is recommended. In this example, even though the pipeline is 6”, a 6” valve is not recommended.

Choose the required voltage, Item and Model Numbers from the Ordering Information Charts below.