94270 Vapor Guard Tank Blanketing Valve

Shand & Jurs 94270 Vapor Guard Tank Blanketing Valve
  • Lower maintenance due to fewer parts

  • Occupies less space, less stress to tank

  • Teflon is inert to most chemicals; extends service life

  • Simplifies and lowers maintenance cost

  • Optimizes flow of blanketing gas


What is Tank Blanketing?
Gas blanketing systems are used to prevent the escape of liquid vapors into the atmosphere or to prevent moisture from entering a tank and contaminating its contents. A tank blanketing valve maintains an inert gas blanket (usually nitrogen or carbon-dioxide) in the vapor space of a pressure-tight liquid storage vessel. This process is accomplished by utilizing a steady high-pressure gas source and the Shand & Jurs Model 94270 "VAPOR GUARD" so that flow is limited to a constant value when the main valve is opened below the set point.

The valve limits the minimum pressure of the gas blanketing to cope with outdoor temperature reductions or pump outs without inbreathing air. When pressure inside the vessel exceeds the valves set point the main valve shuts off. If pressure increases due to outdoor thermal heating, or product pump-ins, the separate conservation vent opens and relieves the excess pressure. One advantage of using the Shand & Jurs "VAPOR-GUARD" is that only one valve is needed to maintain precise blanketing regulation while conventional recovery systems require several regulators to achieve the same results.

How Does it Work?
The Shand & Jurs 94270's compact design allows the valve to be mounted directly on the tank which in turn not only reduces the number of necessary connections, but also possible leak points. Models are available with female thread connections & threaded-on flanges. The 94270 has a balanced, piston operated, main valve so that the set point pressure is virtually unchanged at any given inlet pressure within the specified operating range. The "VAPOR GUARD" has a modulating type action valve that opens and closes automatically, maintaining a closely controlled blanket pressure and gas flow.

The modulating action simplifies the valve design thus increasing reliability and reducing maintenance costs. The "VAPOR GUARD" operates in the closed position whenever the tank pressure is satisfied or exceeds the set pressure. Whenever the sensed pressure decreases, the set pressure spring and diaphragm assembly causes a downward force such that the main valve will open proportionately to control pressure and limited capacity.

Flow Disc Control Port
Each valve is fitted with a percentage flow control port to meet specific calculated gas blanketing flow requirements based on a steady gas pressure supply. Referral to a flow capacity chart is necessary to size each valve for a particular gas blanketing system. Standard flow control ports are available in four options: 25%, 50%, 75% and 100%of the published flow charts to reduce the flow rate to optimum operating conditions.

Set Pressures
Set pressures are available from 0.50" WC to 15.0 psig. Inlet pressures range from 20 to 200 psig.

Theory of Operation/Model 94270
The latest innovations in valve design include a balanced, piston operated, main valve so that the set point is virtually unchanged at any given inlet pressure within the specified operating range. This type of valve is not a pressure reducing regulator, but rather a modulating valve that automatically opens and closes, as needed, to maintain a closely controlled blanket pressure. Modulating action is preferred over pressure regulation because of the simplified valve design and its inherent reliability and maintainability.

Typical operation calls for the valve to operate in the closed position whenever the tank pressure is satisfied or when it exceeds the set pressure. As the sensed pressure decreases, the set pressure spring and diaphragm assembly causes a downward force such that the main valve will open proportionately to control pressure and limit flow capacity.

Should the pressure in the pilot chamber drop to a point where it can no longer hold against the pilot set pressure, the pilot spindle moves downward, causing the pilot to unseat. This creates a flow from the pilot inlet, through a small orifice, out the pilot discharge tube and into the tank. The pressure above the main valve is then reduced by a pressure drop downstream.

When sufficient pressure drop is achieved, the supply pressure will push open the piston and allow the blanketing gas to enter the tank. When the blanketing gas brings the tank pressure up to the set point, the pilot flow then stops and full supply pressure builds above the piston to close the main valve.

NOTE: In order to ensure reliable operation, a filter is required within 6" of valve inlet. This filter must be sized for inlet requirements determined above.