Four Way Flow Reversing Valves

Why Flow Reversal Systems

Power Stations using sea water and raw water to condense the outlet steam from steam turbines have a problem of fouling of the condenser tubes due to weed and marine growth. Marine growth occurs on the cold side of a condensing system, indicating that the small rise in temperature to the warm side is sufficient to kill incipient growth. Based on this, Fouress-Boving have successfully designed and manufactured flow reversal valve system that can prevent condenser tube fouling. This is a major advantage over conventional systems in respect of system down times, ease of maintenance and capital costs.

Basic Constructional Concepts

The Fouress – Boving 4 – way flow reversal valves come with and without cylindrical strainer elements. The valve had inlet and outlet ports for the flow of cooling water into and out of the valve and a pair of transfer ports into and out of the valve for the flow of cooling water to and from the condenser.

Incorporated within the valve body is an elliptically shaped butterfly blade which is alternately positioned to direct the cooling water from the normal onlet side of the condenser to the normal outlet side, thus reversing the flow. By operating in an intermediate position, these valves can be used foe condenser flow regulation, thus eliminating the need of a separate throttling valve in the cooling water circuit.

Figure shows a typical layout off four-way valve to a condenser and figure 2 shows a section through the four-way valve and its main parts.

The elliptical butterfly valve blade pivots about the junction of the longitudinal axis pf the inlet/outlet ports (A &C) and the transfer ports (B &D). The valve blade can be rotated through 90 degree by a manual gearbox or various automatic actuators with adjustable operating times.

[In the position shown, the valve blade connects the inlet port “A” (Pump Flow) to transfer port D (Condenser inlet) and the transfer port “B” (condenser outlet) to outlet port C (Drain )]

Boving conceived a rubber-seated Four way valve as an extension to the principle of uninterrupted seal used in Butterfly Valves to save short-circuited flow through the e valve and thereby, pumping power of CW pumps. The rubber seal round the periphery of the valve blade seals against a seating ring running “corner to corner” around the inside of the valve body casing. A Second seating ring in the body allows the valve blade to seal against its position, i.e., when inlet port “A” is connected to transfer port “B” and transfer port “D” to outlet port “C”. In each position, the blade provides virtually drop tight sealing (a leakage rate of 0.6%).

Designed, Manufactured and Tested to Perfection

The complex stress generated in a 4-way valve due to various loads and pressure was studied using Finite Element Analysis (FEA). The theoretical Valves thus obtained are checked practically through a detailed strain-gauging and three single- element rosette gauges and three single- element gauges at specified node points found critical in FEA.

The Fouress four-way valve is an engineering marvel, with demanding manufacturing requirements. Special jigs and fixtures as well as innovative and unconventional machining processes were employed for the purpose. High integrity fabrication at the Fouress factory in Bangalore with radiographic quality welding and poet-weld heat treatment is carried out to meet the exacting requirements of Super Thermal Power Stations. The imposing end-product was a Four way Valve weighing as much as 16 tones measuring 2500 mm end to end.

Stage wise quality checks are carried out during and after manufacture. Before “Worls Testing: itself, the valve undergoes some 33 stages of inspection, including hydrostatic, seat leakage and blade strength tests apart from a functional/ operation test. And the result have always been impressive. Just to cite one example, the Fouress 4-way Valve recorded a final leakage of less than 2 Liters/hr against a permissible leakage of 100 liters/hr

Anyway you look a it, from concept to commissioning, the Fouress- Boving four – way vale is an engineering marvel and a proud testimony to the company’s excellence in the development of Appropriate Technology for Indian power industry.