Gas Cleaning System - Weak Acid Valves
March 4, 2002

Introduction Ball Valves Butterfly Valves

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Introduction

A variety of valve types and materials are used throughout the weak acid system.  The corrosive nature of weak sulphuric acid requires that special attention be paid to materials of construction to ensure long service life and reliable operation.  The presence of contaminants such as chlorides, fluorides, solids, etc. will also influence the material of construction selected.

In weak acid service attention must be paid to both internal and external corrosion.  External corrosion will occur when process fluids leak or spill onto the valve body.  The exterior of the valve must be resistant to chemical attack to prevent premature failure.  Thermoplastic valves provide the necessary corrosion resistance, both internally and externally.  They are relatively low cost, light weight, easy to install and maintain.

There are some plant operators that prefer lined metallic valves.  Lined metallic valves offer limited external corrosion protection and are much heavier than the thermoplastic valves.  The piping system must be designed for the heavier metallic valve in terms of providing adequate pipe supports.  Un-lined metallic valves are rarely used because highly alloyed materials must be used to provide the necessary corrosion resistance which results in extremely expensive valves.

Flanges should be flat face with full faced gaskets to minimize the chance of flange breakage when the flanges are tightened.

Ball Valves

Ball valves are used for isolation purposes and on/off service only.  They are available in sizes from ½” through to 4”.  

Manufacturer	Chemline
Model	Safe-Bloc® True Union
Size Range	½" to 4"
Body Material	PVC, CPVC, PP, PVDF
Ball Material	PVC, CPVC, PP, PVDF
Seats	PTFE
Seals	EPDM, Viton, CPE, Nitrile, PTFE
Connection	Threaded, Socket, Flanged

CPE - Chlorinated Polyethylene

The selection of materials for the body, ball and seals will depend on the service conditions.

Butterfly Valves

Butterfly valves are used for flow control and regulation.  They are not recommended for isolation purposes.

Manufacturer	Chemline
Model	TB Series
Size Range	1½" to 24"
Body Material	PVC, PP
Disc Material	PP, PVC, CPVC, PVDF
Seat	EPDM, Nitrile, CPE, Hypalon, Neoprene, Viton
Connection	Semi Lug Wafer
Wrench/Lever Operator	1½" to 6"
Gear Operator	8" to 24"

CPE - Chlorinated Polyethylene

The selection of materials for the body, disc and other wetted parts will depend on the service conditions.