Continuous flow or on-off drain traps

Armstrong’s line of snap-action drain traps includes two basic models available in cast iron and forged steel. The floats are light enough to handle light liquids.

Due to the sporadic liquid flow, much of the time the valve in a standard float-type drainer is only slightly opened. If there is fine dirt or grit in the liquid, particles may accumulate and clog the partially open valve. Or they may lodge between the valve and seat, preventing closure. To overcome this problem, a special toggle spring-operated valve is used.

A flat spring attached to the leverage system holds the valve closed until the liquid level is high enough for the buoyancy to exceed the spring force. Then the valve is snapped open, and the accumulated dirt and grit can be flushed through the open valve. When the body is nearly empty, buoyancy is reduced enough to permit the spring to snap the valve closed.

Snap-Action Operation

Filling cycle. (See drawing.) The trap valve has just closed. The spring is bowed to the right, and the float rides high in the water because no force is exerted on the spring. As water enters, the float rises, storing energy in the spring. This increases submergence of the float.

(See drawing.) In this view, the valve is about to open. The float is now more than half submerged, and the spring has assumed a “handlebar mustache” shape. The energy stored in the spring is due to increased displacement of water. A very slight rise in water level causes the spring to snap to the left—instantly opening the valve. (See drawing.) This releases the energy from the spring, and the float again rides high in the water. As the water level drops, the weight of the float bends the spring to the right, causing snap-action closing of the valve before all of the water has been discharged.