Ch 01 Introduction to Valves -...

Ch. I Introduction to Valves

2Training on Valve Technology

1.1. Valve

Valves are mechanical devices specifically designed to direct, start, stop, mix, or regulate the flow, pressure, or temperature of a process fluid.

Berdasarkan atas fungsinya, aplikasinya, dan rancangannya, valve dapat dibedakan ke dalam beragam kelas styles, sizes, dan ragam pressure.

Tipe yang umum ditemukan adalah plug, ball, globe, butterfly, dan gate valves.

Valve dapat dibuat dari berbagai material seperti: steel, iron, plastic, brass, atau sejumlah material paduan khusus lainnya.

Komponen-komponen utama sebuah valve diberikanpada Gbr. 1

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Gbr. 1 Basic components of a valve

The internal elements of a valve are collectively referred to as a valve's trim.

The trim typically includes a disc, seat, stem, and sleeves needed to guide the stem.

A valve's performance is determined by the disk and seat interface and the relation of the disk position to the seat.



Gbr. 2Manual Valve Gbr.3

Control Valve

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Gbr. 5Gate Valve

Gbr. 6Plug Valve

Gbr. 4Ball Valve



Gbr. 7Globe Valve

Gbr. 8Butterfly Valve

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Gbr. 9 Pinch Valve

Gbr. 10 Diaphragm Valve

open throttling closed



1.2 Klasifikasi Menurut Fungsinya

Berdasarkan atas rancangan dan fungsi valve in handling the fluid, valve dapat dibagi ke dalam 3 kelompok: on-off valves, non-return valves, and throttling valves.

On-off valves: handle the function of blocking the flow or allowing it to pass.

Non-return valves: allow one direction flow only.

Throttling valve: allow for regulation of the flow at any point between fully open to fully closed.

One confusing aspect of defining valves by function and its specific valve-body design (plug, ball, globe, gate, butterfly, pinch, etc.)

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1. On-off Valves

Terkadang juga disebut sebagai block valve.

Kelompok valve ini yang umum dijumpai: gate, plug, ball, pressure relief, dan tank-bottom valves.

Jenis on-off valve umumnya hand-operated, walaupun dapat diotomasi dengan tambahan aktuator.

Pressure-relief valves adalah self-actuated on-off valves yang dapat terbuka hanya jika preset pressure dilampaui (mencegah over pressuration).

Pressure-relief valves dibagi menjadi 2: Relief valves, untuk aplikasi pada fluida cair dan safety valves, untuk aplikasi pada fluida gas.



Gbr. 11 Pengetesan pressure-relief valve

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2. Non-return Valves

Nonreturn valves memungkinkan fluida untukmengalir ke suatu arah yang diinginkan (hanya satu arah saja).

Semua check valves termasuk ke dalam kelompoknonreturn valves.

Valve jenis ini digunakan untuk mencegah terjadinyabackflow yang tidak diinginkan.

Contoh aplikasi: untuk melindungi instalasi pompaatau kompresor dari backflow saat shut down.

Nonreturn valves juga digunakan dalam sistem proses dengan variasi tekanan yang harus dijaga secara terpisah.



Gbr. 12 Piston check valve dalam bidang migas

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3. Throttling Valves

Valve jenis ini digunakan untuk mengatur aliran, temperatur, atau tekanan.

Operasi throttling valves: manual (handwheel or lever) atau dengan kontrol otomatis, Gbr. 13(a).

Pressure regulators adalah throttling valve yang memvariasikan posisi valve untuk menjaga tekanan di hilir valve tetap konstan, Gbr. 13(b)

Automatic control valves atau control valves is a term commonly used to describe valves that capable of varying flow conditions to match the process requirements dilengkapi dengan actuator.



Gbr. 13 Contoh throttling valves

(a) Globe control valve(b) Pressure regulator

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1.3 Klasifikasi Menurut Aplikasinya

Tiga klasifikasi valve menurut aplikasinya: general service valve, special service valves, dan severe service valves.

General service valves: valve yang dapat digunakan pada banyak aplikasi tanpa perlumodifikasi.

Special service valves: valve yang dirancang khusus untuk aplikasi tertentu/spesifik.

Severe service valves: valve yang dirancang khususuntuk mencegah efek samping pada aplikasi yang sulit.



1. General Service Valves

Termasuk ke dalam kelompok ini adalah valve yang dirancang untuk mayoritas aplikasi yang umum: Lower-pressure: ANSI Class 150 s/d 600. Moderate-temperature rating: -50oF s/d 650oF. Non-corrosive fluid Common pressure drop yang tidak menyebabkan

kavitasi atau flashing.

Dalam perancangannya, valve tipe ini dibuat dengan level interchangeability dan flexibility yang tinggi sehingga memiliki rentang aplikasi yang lebar.

Material body: baja karbon atau baja tahan karat.

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Gbr. 14 Example of two general service valves

Manual Otomatis



2. Special Service Valves

Special service valves is a term used for custom-engineered valves that are designed for a single application that is outside normal process application.

Valve jenis ini biasanya untuk aplikasi pada temperatur tertentu, tekanan tinggi, atau medium yang korosif.

Gbr. 15 memperlihatkan contoh sebuah control valve yang dirancang dengan sweep-style body dan trim dari keramik untuk aplikasi yang erosif dengan pasir dan tekanan yang tinggi.

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Gbr. 15 Sweep-style globe valve usedin erosive mining application



3. Severe Service Valves

Severe service valves are valves equipped with special features to handle volatile applications, such as high pressure drops that result in severe cavitation, flashing, choking, or high noise levels.

Pada kondisi tertentu sering dibutuhkan special actuation untuk mengatasi gaya yang terjadi.

Gbr. 16 shows severe service valve to handle 1100oF (593oC) liquid-sodium application with multistage trim to handle a high pressure drop and a bonnet with special cooling fins.

The electro-hydraulic actuator is capable of producing almost 89 ton of thrust.

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Gbr. 16 Severe service valve designed to handle high-pressure drop, high temperature liquid-sodium application



1.4 Klasifikasi Menurut Gerakan

Some users classify valves according to the mechanical motion of the valve: linear or rotary.

Linear valves are known for their simple design, easy maintenance, and flexibility with more size, pressure class, and design options than other motion classification the most common type of valves.

Linear-motion valves (linear valves) memiliki rancangan sliding-stem yang mendorong closure element saat valve membuka atau menutup.

Gate, globe, pinch, diaphragm, split-body, three-way, and angle valves semuanya masuk ke dalam kelompok linear valves.

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Rotary-motion valves (rotary valves) use a closure element that rotates-through a quarter-turn or 90o

range-to open and close the flow.

Rotary valves are usually smaller in size and weigh less than comparable linear valves.

The applications is limited to certain pressure drops and are prone to cavitation and flashing problem.

As rotary-valve designs have matured, they have overcome these inherent limitations and now being used at an increasing rate.

Ball, plug, butterfly valves semuanya masuk ke dalamkategori rotary-motion valves.



1.5 Klasifikasi Menurut Port Size

Valves with internal flow equal to the full area of the inlet port.

Jenis ini utamanya digunakan sebagai on-off and blocking service valves, dimana aliran harus distopatau dialihkan.

Full-port valves memungkinkan penggunaan pig dalam pipeline.

The pig is a self-driven (or flow-driven) mechanism designed to clean the inside of the pipeline and to remove any process buildup or scale.

1. Full-Port Size

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Reduced-port valves are those whose closure elements restrict the flow (area of closure element is less then the area of the inside diameter of pipeline.)

Pembatasan aliran menyebabkan terjadinya pressure drop saat aliran melewati closure element dan sebagian tekanan dapat direcovery setelahnya.

The primary purpose of reduced-port valves is to control the flow through reduced flow or throttling, which is defined as regulating the closure element to provide varying levels of flow at a certain opening of the valve.

2. Reduced-Port Size



1.6 Common Piping NomenclatureValve and piping nomenclature has been heavily influenced by imperial system (ANSI standards).

The psi is used to refer to pressure and NPS to refer to valve and pipe size (in inches across the pipes inside diameter.

In many countries, outside of the USA, valve and piping nomenclature is based on the International System of Units (metric system) from ISO.

Typically metric valve measurement are called out in millimeter and pressure are noted in kilopascal (kPa) (or bar).

ISO standards refer to pipe diameter as nominal diameter (DN) and pressure rating as nominal pressure (PN).

Tables 1 and table 2 provide quick reference for both ANSI and ISO standards.

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1506.0

1004.0

803.0

652.5

502.0

401.5

321.25

251.0

200.75

150.5

60.25

DN (mm)NPS (in.)

120048.0

100042.0

90036.0

60024.0

50020.0

45018.0

40016.0

35014.0

30012.0

25010.0

2008.0

DN (mm)NPS (in.)

Table 1 NPS versus DN



7004500

4002500

2501500

160900

100600

40300

16150

(allowable pressure in bar)(pounds of force per square

inch of surface area)

Nominal Pressure (PN)ANSI Pressure Class

Table 2 ANSI Pressure Class vs. Nominal Pressure*)

Note:PN is an approximation to the corresponding ANSI pressure class, and should not be used as an exact correlation between two standards.

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Reference

Skousen, P.L., Valve Handbook, McGraw-Hill, USA, 1998.

Fisher, Control Valve Handbook, Fisher Control International, USA, 2001.



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