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Bermad Model 735 - Surge Anticipating Control Valve

The Model 735-M Surge Anticipating Valve is an off-line, hydraulically operated, diaphragm actuated valve. The valve, sensing line pressure, opens in response to the pressure drop associated with abrupt pump stoppage. The pre-opened valve dissipates the returning high-pressure wave, eliminating the surge. The Model 735-M smoothly closes drip tight as quickly as the relief feature allows while preventing closing surge. The valve also relieves excessive system pressure.

735 - XXX

Features and Benefits

  • Replaces surge air vessels
    - Relieves surge, fail-safe open
    - Minimal maintenance
    - Economy of space
    - Lower investment & maintenance costs
    - Especially economic for higher pressure ratings
  • Line pressure driven
    - Independent operation
    - No motor required
    - Long term drip tight sealing
    - Adjustable hydraulic actuation
  • Double chamber
    - Moderated valve closing (no surges)
    - Protected diaphragm
  • In-line serviceable – Easy maintenance
  • Obstacle free, full bore – Uncompromising reliability
  • Balanced seal disk – High flow capacity

Major Additional Features

  • Solenoid control – 735-55-M
  • Sensing diaphragm (for sewage) – 735-Md
  • Electric override for fire protection – FP-730-59
  • Quick pressure relief valve – 73Q


The abrupt stopping of a pump produces a pressuredrop as the traveling column of water, with its inherentmomentum, continues to travel along the line,generating severe low pressure.When the traveling column of water loses itsmomentum, it travels back towards the pump. Shouldit hit the closed check valve, a very high pressuresurge is created and travels throughout the systemas a damaging wave at velocities of up to "Mach 4".No quick relief valve can react quickly enough toeliminate it.

Eliminating surge requires anticipation and pre-action. The Model 735-M is well suited to this task. The Low Pressure (LP) pilot [1] senses the initial pressure drop and opens. This immediate reaction allows remaining line pressure to quickly open the main valve.

The already opened Model 735-M releases the returning column of water, minimizing the line pressure rise. Should the relief rate be insufficient, and the pressure exceed the High Pressure (HP) pilot [2] setting, the pilot immediately opens, further opening the main valve.

As system pressure stabilizes again at static pressure, both pilots close and the main valve begins closing. Should line pressure rise during main valve closing, the HP pilot briefly stops the process, preventing the pressure from continuing to rise. The flow stem [3] limits the relief flow to prevent column separation and preserve closing pressure.

Cock valve [4] serves for selecting operating and sensing source:

  • Directly from main discharge line - Recommended (see “Typical Application”)
  • From Model 735-M inlet

Typical Applications

In this system, a pump battery supplies the main line through a manifold. The Model 735-M:

  • Eliminates surge upon power failure
  • Provides surge free switching between “on-duty” pumps
  • Closes smoothly according to pilot setting

Bermad Surge Analysis Program – “BERSAP II”

Surge is the result of many factors: designed flow rate, pumping system, main line characteristics, etc. By using advanced mathematics and computer software, BERMAD’s experienced engineers can perform the desired analysis. For best analysis, all of the following data is required.

  • Main Line
    - Line Profile (Chainage), elevations at accumulated length
    - Internal diameter
    - Length
    - Material
    - Wall thickness
  • Pumps
    - Pump curve(s)
    - Max. number of pumps in simultaneous operation
    - Type of non-return valve
  • System
    - Max. designed flow rate
    - Max. and min. levels at suction and at delivery reservoirs

For systems with multiple pumping stations and/or multiple consumers along the supply line, the following data is also required:

  • System layout including pumping station, and consumer locations, and characteristics
  • Head Gradient Line (HGL) for each and every node based on “Network-Solver” analysis

This surge analysis indicates that without protection the system is exposed to:

  • Pressure of ~32 bar (see max. pressure envelope line)
  • Vacuum conditions (see min. pressure envelope line)

Simulated surge protection recommends:

  • Two Model 735-M valves installed in parallel at the pumping station
  • Five Non-Slam Air Valves installed along the line

With full surge protection, the simulation shows no surge and minimal vacuum.

  • Pressure at max. of ~19 bar (see max. pressure envelope line)
  • No appreciable vacuum (see min. pressure envelope line)
Any pipeline design requires air valves to admit air under vacuum conditions and to release air under pressure. The size, type and location of these air valves should consider surge protection requirements.

Engineer Specifications

The Surge Anticipating Valve shall open in response to the pressure drop associated with abrupt pump stoppage to dissipate the returning high pressure wave, eliminating the surge. It shall smoothly close drip tight as quickly as the relief feature allows, while preventing closing surge. The valve shall also relieve excessive system pressure.

Main Valve: The main valve shall be a center guided, diaphragm actuated globe valve of either oblique (Y) or angle pattern design. The body shall have a replaceable, raised, stainless steel seat ring. The valve shall have an unobstructed flow path, with no stem guides, bearings, or supporting ribs. The body and cover shall be ductile iron. All external bolts, nuts, and studs shall be Duplex® coated. All valve components shall be accessible and serviceable without removing the valve from the pipeline.

Actuator: The actuator assembly shall be double chambered with an inherent separating partition between the lower surface of the diaphragm and the main valve. The entire actuator assembly (seal disk to top cover) shall be removable from the valve as an integral unit. The stainless steel valve shaft shall be center guided by a bearing in the separating partition. The replaceable radial seal disk shall include a resilient seal and shall be capable of accepting a V-Port Throttling Plug by bolting.

Control System: The control system shall consist of two adjustable 2-way pilots, a needle valve, a flow stem, a cock valve, and a filter. All fittings shall be forged brass or stainless steel. The assembled valve shall be hydraulically tested.

Quality Assurance: The valve manufacturer shall be certified according to the ISO 9001 Quality Assurance Standard. The main valve shall be certified as a complete drinking water valve according to NSF, WRAS, and other recognized standards.

Technical Data

Dimensions and Weights

Main Valve

Valve Patterns: “Y” (globe) & angle

Size Range: 11/2–32” (40-800 mm)

End Connections (Pressure Ratings): Flanged: ISO PN16, PN25

(ANSI Class 150, 300)

Threaded: BSP or NPT

Others: Available on request

Working Temperature:

Water up to 80°C (180°F)

Standard Materials:

Body & Actuator: Ductile Iron

Internals: Stainless Steel, Bronze & coated Steel

Diaphragm: NBR Nylon fabric-reinforced

Seals: NBR

Coating: Fusion Bonded Epoxy, RAL 5005 (Blue) NSF & WRAS approved or Electrostatic Polyester Powder, RAL 6017 (Green)

Control System

Standard Materials:

Accessories:mBronze, Brass, Stainless Steel & NBR

Tubing: Copper or Stainless Steel

Fittings: Forged Brass or Stainless Steel

Pilot Standard Materials:

Body: Brass, Bronze or Stainless Steel

Elastomers: NBR

Springs: Galvanized Steel or Stainless Steel

Internals: Stainless Steel

Pilot Valve Selection

Flow Chart

How to Order

Please specify the requested valve in the following sequence: (for more options, refer to Ordering Guide)

PDF Datasheets

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Engineering Data*

2D CAD Drawing

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Engineering Data*
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Product code

Bermad Model 735 - Surge Anticipating Control Valve

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