Chap 11 Types of Pipes and Valves PDF

11-1 CHAPTER 11 TYPES OF PIPES, FITTINGS, VALVES AND ACCESSORIES FOR FILTRATION SYSTEM 1 Pipes Commonly Used In an AF Insta...

11-1 CHAPTER 11 TYPES OF PIPES, FITTINGS, VALVES AND ACCESSORIES FOR FILTRATION SYSTEM 1 Pipes Commonly Used In an AF Installations Water is a good solvent and chemicals can dissolve in it quite easily. In an AF, a few chemicals are added to achieve sanitized quality, chemicals commonly used are: Hypochlorites, to disinfect AF water Acids and alkalis, to adjust the pH level of AF water Algaecides to prevent algae growth Alumina sulphate (Alum) added for flocculation As such the equipment, pipes and valves installed in an AF system must be resistant to attacks by and harmful reactions with the chemicals used. 1.1 Ductile Iron Cement Lined Pipe “Ductile” means capable of deformation. Though made from cast iron which is brittle, the material “ductile cast iron” is not as rigid, and has the capacity to yield, and that makes it strong. The pipe, conforming to Class K9 of BS 4772, has cement mortar lined bore and epoxy resin coating in the joint area. This ensures that they are resistant to corrosion caused by AF water. Externally, ductile iron pipe is coated with a metallic zinc coating and a finishing coat of bitumen or epoxy resin of 70 to 100µm in thickness. 1.1.1 Advantages and Disadvantages of Ductile Iron Pipes Ductile iron pipe has the following characteristics suitable for use in AF pipework: can withstand high internal pressure and practically all bearing loads from the ground and traffic easily jointed joints are up to 5o flexible Being a heavy pipe, its inherent disadvantage would be the need to use thrust blocks along the pipe line where thrust force is generated. 1.1.2 Corrosion Protection of Ductile Iron Pipes Ductile Iron Pipes internal protection consists of centrifugally spun cement mortar producing a well bonded, dense and uniform layer with smooth finish, enhancing flow and reducing head losses. Portland cement has chemically alkaline reaction property resulting in precipitate clogging the pores of the mortar, preventing further passage of water.  11-2 Through these reactions, the lining provides a physical as well as a chemical barrier to the corrosive water. However acids can dissolve concrete. The degree of dissolution depends on the amount of acid, and weak acids, e.g. carbonic acid formed from rain falling through the atmosphere, can therefore be a greater risk then a strong acid. 1.1.3 Jointing of Ductile Iron Pipes Ductile iron pipes are commonly jointed with: push-on rubber ring joint mechanical joint flanged joint Figure 11-1: Ductile iron pipe joints, in order: Push-on, mechanical and flanged joint 1.2 Galvanised Steel Pipe with Polyethylene (PE) Lining Galvanized steel pipes approved for use conform to BS 1387. Galvanised steel is steel that has been covered with a layer of zinc metal. During galvanizing, steel is immersed in a molten zinc bath, ensuring a tough, uniform barrier coating. Zinc's natural corrosion resistance provides long-term protection, even in outdoor environments. Apart from preventing water corrosion, it is equally effective in dry, indoor environments resisting the attack of wind, water and road salts. 1.2.1 Advantages and Disadvantages of Galvanised Steel Pipes Galvanised steel pipe has the following characteristics suitable for use in AF pipework: strong, withstanding high internal pressure and heavy grade Class ‘C’ (of BS 1387) pipe could bear loads from the ground and traffic flexible easily jointed Corrosion is a major concern with steel pipings, some allowance can be made by using the thicker-walled medium grade Class ‘B’ (of BS 1387) piping. However, this approach is valid only for uniform corrosion rates. AF water with the various concentrations of dissolved chemicals or gases can result in pitting or crevice corrosion. If the potential exists for this type of attack, or if the fluid has been exposed to the air before entering the system, carbon steel should be the material of last resort, considering corrosion and scaling concerns, resulting in galvanized steel piping being used primarily on the clean loop side of the circulatory system. Another distinct disadvantage is external corrosion that could result in a number of failures. The potential for external corrosion of metallic pipe systems should be considered for all direct buried installations. Various soil types, presence of ground-  11-3 water, and induced current fields from power lines may accelerate external pipe corrosion and early piping failure. Buried pipes should be protected with a suitable wrapping e.g. pipework wrapped with a mastic saturated with an asphalt material to provide a seal, or install cathodic protection. Figure 11-2: Galvanised Steel pipe with corrosion protective wrapping 1.2.2 Corrosion Protection of Galvanised Steel Pipes Internally, galvanized steel pipe is lined with plastics such as polyethylene (PE) or unplasticised polyvinyl chloride (uPVC) to withstand internal corrosion. Characteristics of PE are: Light in weight Flexible Non-corrosive Non-toxic High abrasion resistance High chemical resistance High resilience Low head loss Practically unlimited life in water 1.2.3 Jointing of Galvanised Pipes Galvanised steel pipes are commonly jointed with threaded joint. Figure 11-3: Galvanised Steel pipe threaded joint Figure 11-4: Galvanised Steel pipework and fittings  11-4 1.3 Unplasticised Polyvinyl Chloride (uPVC) Pipe Unplasticised polyvinyl chloride (uPVC) is one of the most widely used thermoplastic materials for pipe installations. It has good flow characteristics because of the smooth bore, and it also has good resistance to abrasion. The grade used for AF installation conforms to Class AW (JIS K-6741-75) Class D (≤12 bar) and Class E (≤15 bar) of SS 141 1.3.1 Advantages and Disadvantages of uPVC Pipe uPVC pipe has the following characteristics suitable for use in AF pipework: excellent, in terms of corrosion resistance. odourless and tasteless making it is suitable for conveying potable water excellent chemical resistance, being resistant to most solutions of acids, alkalis, salts and solvents that can be mixed with water light in weight, easy to join together making uPVC a good alternative to the more traditional materials. The disadvantage of uPVC pipe is that it softens with heat, and deteriorates in characteristics when exposed to sunlight. It is also has low impact strength, not strong enough to withstand loading from soil and traffic if buried below ground, unless it is built with concrete foundation and surround. For suspended pipes, definitely more pier supports and hangers are required, as compared with stronger and more rigid pipes made of iron and steel. 1.3.2 Jointing of uPVC Pipes uPVC pipes can be jointed using the following joints: solvent cement joint threaded joint flange joint rubber ring joint For smaller pipes, solvent cement is most commonly used. Occasionally, AW gauge pipes are threaded. Valves come in compression joint using rubber rings. For large diameter pipes flange joints are used. Figure 11-5: uPVC fittings in their various forms Figure 11-6: Solvent Cement joint  11-5 1.3.3 Solvent Cements for Plastic Pipes Pipe Solvent Cement 1 ABS (Acrylonitrile- Methyl Ethyl Ketone Butadiene-Styrene) 2 uPVC (unplasticised Tetrahydrofuran Polyvinyl Chloride) 3 PE (Polyethylene) Mechanical joint e.g. Butt fusion using heat 4 SR (Styrene rubber) Toluene Table 1: Plastic pipes and their solvent cements 1.4 Acrylonitrile-Butadiene-Styrene (ABS) Pipe ABS (Acrylonitrile Butadiene Styrene) pipe conforming to BS 5391, is a highly rated thermoplastic pipe. Used in preference to PVC for high ( 50°-70°C/120° - 160°F ) or low ( less than –20°C/-4°F ) temperatures. It is hard for plastic and reasonably tough and has a good gloss finished. 1.4.1 Advantages and Disadvantages of ABS Pipe ABS pipe has the following characteristics suitable for use in AF pipework: easily bonded impact resistant at low temperature rigid and suitable for non-pressurized water. non-toxic. good chemical resistance against most diluted inorganic acids, salts, animal fats and oils and organic acids. It is not resistant to organic solvents, alcohol, petrol, acetic acid or vegetable oils. It also has poor UV resistance unless protected. 1.4.2 Jointing of ABS Pipes ABS pipe and uPVC pipe use similar joints and jointing methods. Its fittings also come in similar forms. (See diagram below.) The common joints used are: solvent cement joint threaded joint flange joint rubber ring joint Figure 11-7: ABS pipe cement fittings  11-6 2 Reasons for using Pipes of different materials (a) Savings: In terms of jointing and installing the pipeork. For example jointing uPVC pipes is faster and cheaper then galvanized steel pipes. (b) Strength: In a place where the load bearing on the pipe is heavy, then steel pipe will have to be used. Pipes that run under the AF and driveways should be of ductile cast iron pipes. Valves for large diameter pipes will need rigidity e.g. 300mm diameter, valves used should be made of ductile cast iron. 3 Common Valves used in AF Circulatory System Numerous valves are used in an AF circulatory system. Common valves used are: Gate valve Globe valve Check valve Ball valve Air relief valve 3.1 Gate valve Gate valve, also known as sluice valve is an on-off valve, i.e. either in fully opened or fully closed position. Gate valve has the least impedance to flow property when fully opened. Gate valve produces the heaviest water hammer. It should not be used as throttling device. Gate valves (≥) equal or larger than 80mm conform to BS 5163. For those smaller (≤) should conform to BS 3464. Figure 11-8: Gate valves Figure 11-9: Globe valves  11-7 3.2 Globe valve Globe valve is a lift valve. It is suitable for throttling, modulating flow in delivery line, however, flow properties and pressure are affected. Globe valves (≥) equal or larger than 80mm conform to BS 1873. 3.3 Check valve Check valve is a one-way valve and is used for preventing reverse flow. Common forms of check valves are: Flap type conforming to BS 4090, is more suitable for horizontal installation. Disc type conforming to BS 4090, is more suitable for vertical installation. Dual disc (or butterfly) type conforming to API 594 or BS 4090 is suitable for horizontal and vertical installation. Flow Flow Flow Open Flow Figure 11-10: Check valves 3.4 Ball valve Ball valves are normally quarter turn quick action straight through flow valves that have a round closure element with matching rounded seats that permit uniform sealing stresses. A Ball valve is popular in many situations where tight shut off is required. The type of seat can vary with the valve pressure rating and materials of construction. Some valve seats may be composed of single molded forms, while other seats with higher-pressure ratings could incorporate a trunnion design where each face of the ball is separately sealed. Ball valve can be used for on-off as well as throttling. They could be made from brass or ABS and for throttling, impedance to flow properties is very much reduced, compared to with gate valve.  11-8 For the ABS type, it comes with solvent cement or threaded connection. Ball valves conform to: ABS type, BS 3505 or BS 3506 Brass type, BS 5154 or SS 75 Figure 11-11: Ball (plug) valves Figure 11-12: Air release valve 3.5 Air release valve Air Release Valves function to release air pockets that collect at each high point of a full pressured pipeline. Air release valves can open against internal pressure, because the internal lever mechanism multiplies the float force to be greater than the internal pressure. This greater force opens the orifice whenever air pockets collect in the valve. Air Release Valves are essential for pipeline efficiency and water hammer protection. Air Release Valves conform to BS 4504. 4 Automatic and Manual Filtration The most number of valves are found at the filter units. Valves are turned on and off to direct water to flow into the filter units for normal circulation, re-direct the water to flow reverse for backwashing and rinsing etc. Here, the process can be made easier by automating the on and off operations of the valves by actuating them with pneumatic, hydraulic or electric actuators, activated by pressure sensor sensing the water pressure or timer to perform, for example, backwashing at regular intervals. 4.1 Automatic Filtration Automating the valves in DE filters is not so easy though possible. Automating a sand filter would be much easier. Individual valve is electrically actuated to open or close to allow normal circulatory flow and backflow. The advantages of automated operation are: water cleanliness is assured savings on man-hour, in particular when there are a few filters to backwash and maintain human errors are eliminated  11-9 Automatic filtration has its drawbacks, mainly the cost to: employ higher level trained personnel to operate and maintain the system install sophisticated equipment to monitor water quality accurately and constantly install and maintain the automation equipment in addition to AF equipment The unpredictability of bather load and other variables such as weather could upset the normal operation. In adverse conditions or situation, response from automated equipment might be slow. In a manual filtration system, valves are hand operated to configure the valve for normal circulatory flow and backwash flow. Its advantages are: backwash, normal flow and even closure of the AF can be decided by the person-in-charge present at site, adopting immediate appropriate responses as required by the conditions or situation at that time responsibility is accountable operation cost is less as lower level skilled labour can manage the work, and the system works without expensive automation equipment Besides being time consuming, the other main drawback of manual filtration is the human factor, meaning the person-in-charge at site must be competent and responsible. Figure 11-13: An electrically operated multiport valve 