By Gautam Shah  


Pressure Cookers with Inner and Outer Lid sealing


These are pressure doors or plug doors. As the pressure inside increases the shutter leaf presses itself harder on the outer or inner seams. The bulge (convex) shape of the lid adds to the surface area for greater efficiency of sealing. A well-designed plug door relies only on the strength of the wall around (forming the seams) it. Plug doors like situations also occur on high altitude flying passenger air-crafts. Due to the higher air pressure within the aircraft cabin than of the surrounding atmosphere the door seals itself. This prevents the opening of a plug door on a pressurized aircraft. However, at lower altitudes or on landing the decompression, allows a door to be opened. Rapid Transit Series buses feature front and rear plug doors.

Hatch door with Hinge mechanism


Front loading Washing Machine Hatch Door

These are doors for entry into large tanks, reservoirs, boats, submarines, car roofs, washing machines and space vehicles. These doors like openings are very small size, just circumference of a person, and are placed in a wall or roof (though at places the wall or roof definitions are irrelevant). The door or the lid is either hinged one or is a free unit. The hatches have a glass lid, glass a view window, but all in bulged form. The hatches are required to fit snugly so have air-water tight gasket lining. The door closing is secured through multiple snap-clamps or bolts. The opening and shutting are often triggered by the pressure conditions on either side of the lid. The hatches in walls are slightly raised, whereas the in floors these have a marked and raised perimeter or are fitted in level with the surrounding structure. Hatch doors are designed as less frequently used opening system, but snug-closing is important. Ship and aircraft windows which are fixed and are round edged openings are also called hatch openings. Automobiles also have a roof level hatch openings.

Space Module Hatch Door

Submarine Hatch Door


These are similar to hatched openings, but could be as large as the mouth of the reaction vessel, or of functional size that allows addition of raw materials or drawing out a batch sample. These shutters are rim over the rim fitting type or flat-edge fitting systems where no internal pressure generation occurs. Otherwise, for pressure reaction vessels, the shutter systems are similar to domestic kitchen pressure cookers.

Chemical reaction vessels


A paint tin lid is a common example of a non plug door. It relies on the wedge shape of the seam edge. Canvas sheets in artists’ frames are held by clamps.

Paint Tin Lid


Valves have a closing diaphragm or a plunger to seal an opening and thereby cut the flow. Butter fly valves have a central pivoting diaphragm similar to wings of a butterfly. Ball valves have a ball which gets displaced by the pressure of liquid or gas, but shuts the opening by falling down due to gravity, and thereby prevent any floe in reverse direction.

Butterfly Valve


Old style Camera shutters have multiple flaps, which is pin pivoted at the outer edge, whereas the inner edges overlap. The flaps open and close very simultaneously and quickly by a rotating mechanism that actuates the outer edge of the pivot. The inner edges form a polygon or nearly a circle, thus giving a smooth edge to the picture being shot. New technology cameras have CCD devices which are activated by an electrical impulse.

Camera Shutter