- •Contents
- •Foreword
- •Preface
- •1 Materials in the Lab
- •2 Measurement
- •3 Joints, Stopcocks, and Glass Tubing
- •4 Cleaning Glassware
- •5 Compressed Gases
- •6 High and Low Temperature
- •7 Vacuum Systems
- •8 The Gas-Oxygen Torch
- •APPENDIX
- •Appendix A Preparing Drawings for a Technician
- •Index
- •Foreword
- •Preface
- •For the Second Edition
- •Please note:
- •1 Materials in the Lab
- •1.1 Glass
- •1.1.1 Introduction
- •1.1.2 Structural Properties of Glass
- •1.1.3 Phase Separation
- •1.1.4 Devitrification
- •1.1.5 Different Types of Glass Used in the Lab
- •1.1.6 Grading Glass and Graded Seals
- •1.1.7 Separating Glass by Type
- •1.1.9 Stress in Glass
- •1.1.11 Tempered Glass
- •1.1.13 Limiting Broken Glass in the Lab
- •1.1.14 Storing Glass
- •1.1.15 Marking Glass
- •1.1.16 Consumer's Guide to Purchasing Laboratory Glassware
- •1.2 Flexible Tubing
- •1.2.1 Introduction
- •1.2.2 Physical Properties of Flexible Tubing
- •1.3 Corks, Rubber Stoppers, and Enclosures
- •1.3.1 Corks
- •1.3.2 Rubber Stoppers
- •1.3.3 Preholed Stoppers
- •1.3.4 Inserting Glass Tubing into Stoppers
- •1.3.5 Removing Glass from Stoppers and Flexible Tubing
- •1.3.6 Film Enclosures
- •1.4 O-Rings
- •1.4.2 Chemical Resistance of O-Ring Material
- •1.4.3 O-Ring Sizes
- •2 Measurement
- •2.1 Measurement: The Basics
- •2.1.1 Uniformity, Reliability, and Accuracy
- •2.1.2 History of the Metric System
- •2.1.3 The Base Units
- •2.1.4 The Use of Prefixes in the Metric System
- •2.1.5 Measurement Rules
- •2.2 Length
- •2.2.1 The Ruler
- •2.2.2 How to Measure Length
- •2.2.3 The Caliper
- •2.2.4 The Micrometer
- •2.3 Volume
- •2.3.1 The Concepts of Volume Measurement
- •2.3.2 Background of Volume Standards
- •2.3.4 Materials of Volumetric Construction #1 Plastic
- •2.3.5 Materials of Volumetric Construction #2 Glass
- •2.3.6 Reading Volumetric Ware
- •2.3.7 General Practices of Volumetric Ware Use
- •2.3.8 Calibrations, Calibration, and Accuracy
- •2.3.9 Correcting Volumetric Readings
- •2.3.10 Volumetric Flasks
- •2.3.11 Graduated Cylinders
- •2.3.12 Pipettes
- •2.3.13 Burettes
- •2.3.14 Types of Burettes
- •2.3.15 Care and Use of Burettes
- •2.4 Weight and Mass
- •2.4.1 Tools for Weighing
- •2.4.2 Weight Versus Mass Versus Density
- •2.4.3 Air Buoyancy
- •2.4.5 Balance Location
- •2.4.6 Balance Reading
- •2.4.7 The Spring Balance
- •2.4.8 The Lever Arm Balance
- •2.4.9 Beam Balances
- •2.4.10 Analytical Balances
- •2.4.11 The Top-Loading Balance
- •2.4.12 Balance Verification
- •2.4.13 Calibration Weights
- •2.5 Temperature
- •2.5.1 TheNature of Temperature Measurement
- •2.5.2 The Physics of Temperature-Taking
- •2.5.3 Expansion-Based Thermometers
- •2.5.4 Linear Expansion Thermometers
- •2.5.5 Volumetric Expansion Thermometers
- •2.5.7 Thermometer Calibration
- •2.5.8 Thermometer Lag
- •2.5.9 Air Bubbles in Liquid Columns
- •2.5.10 Pressure Expansion Thermometers
- •2.5.11 Thermocouples
- •2.5.12 Resistance Thermometers
- •3.1 Joints and Connections
- •3.1.1 Standard Taper Joints
- •3.1.2 Ball-and-Socket Joints
- •3.1.3 The O-Ring Joint
- •3.1.4 Hybrids and Alternative Joints
- •3.1.5 Special Connectors
- •3.2 Stopcocks and Valves
- •3.2.1 Glass Stopcocks
- •3.2.2 Teflon Stopcocks
- •3.2.3 Rotary Valves
- •3.2.4 Stopcock Design Variations
- •3.3.1 Storage and Use of Stopcocks and Joints
- •3.3.2 Preparation for Use
- •3.3.3 Types of Greases
- •3.3.4 The Teflon Sleeve
- •3.3.5 Applying Grease to Stopcocks and Joints
- •3.3.6 Preventing Glass Stopcocks and Joints from Sticking or Breaking on a Working System
- •3.3.7 Unsticking Joints and Stopcocks
- •3.3.8 Leaking Stopcocks and Joints
- •3.3.9 What to Do About Leaks in Stopcocks and Joints
- •3.3.10 General Tips
- •3.4 Glass Tubing
- •3.4.1 The Basics of Glass Tubing
- •3.4.2 Calculating the Inside Diameter (I.D.)
- •3.4.3 Sample Volume Calculations
- •4 Cleaning Glassware
- •4.1 The Clean Laboratory
- •4.1.1 Basic Cleaning Concepts
- •4.1.2 Safety
- •4.1.3 Removing Stopcock Grease
- •4.1.4 Soap and Water
- •4.1.5 Ultrasonic Cleaners
- •4.1.6 Organic Solvents
- •4.1.7 The Base Bath
- •4.1.8 Acids and Oxidizers
- •4.1.9 Chromic Acid
- •4.1.10 Hydrofluoric Acid
- •4.1.11 Extra Cleaning Tips
- •4.1.12 Additional Cleaning Problems and Solutions
- •4.1.13 Last Resort Cleaning Solutions
- •5 Compressed Gases
- •5.1 Compressed GasTanks
- •5.1.1 Types of Gases
- •5.1.2 The Dangers of Compressed Gas
- •5.1.3 CGA Fittings
- •5.1.4 Safety Aspects of Compressed Gas Tanks
- •5.1.5 Safety Practices Using Compressed Gases
- •5.1.6 In Case of Emergency
- •5.1.7 Gas Compatibility with Various Materials
- •5.2 The Regulator
- •5.2.1 The Parts of the Regulator
- •5.2.2 House Air Pressure System
- •5.2.4 How to Use Regulators Safely
- •5.2.6 How to Purchase a Regulator
- •6 High and Low Temperature
- •6.1 High Temperature
- •6.1.1 TheDynamics of Heat in the Lab
- •6.1.2 General Safety Precautions
- •6.1.3 Open Flames
- •6.1.4 Steam
- •6.1.5 Thermal Radiation
- •6.1.6 Transfer of Energy
- •6.1.7 Hot Air Guns
- •6.1.8 Electrical Resistance Heating
- •6.1.9 Alternatives to Heat
- •6.2 Low Temperature
- •6.2.1 TheDynamics of Cold in the Lab
- •6.2.2 Room Temperature Tap Water (=20°C)
- •6.2.8 Safety with Slush Baths
- •6.2.9 Containment of Cold Materials
- •6.2.10 Liquid (Cryogenic) Gas Tanks
- •7 Vacuum Systems
- •7.1 How to Destroy a Vacuum System
- •7.2.1 Preface
- •7.2.2 How to Use a Vacuum System
- •7.2.4 Pressure, Vacuum, and Force
- •7.2.5 Gases, Vapors, and the Gas Laws
- •7.2.6 Vapor Pressure
- •7.2.7 How to Make (and Maintain) a Vacuum
- •7.2.8 Gas Flow
- •7.2.9 Throughput and Pumping Speed
- •7.3 Pumps
- •7.3.1 The Purpose of Pumps
- •7.3.2 The Aspirator
- •7.3.3 Types and Features of Mechanical Pumps
- •7.3.4 Connection, Use, Maintenance, and Safety
- •7.3.5 Condensable Vapors
- •7.3.6 Traps for Pumps
- •7.3.7 Mechanical Pump Oils
- •7.3.8 The Various Mechanical Pump Oils
- •7.3.9 Storing Mechanical Pumps
- •7.3.11 Ultra-High Vacuum Levels Without Ultra-High
- •7.3.12 Diffusion Pumps
- •7.3.13 Attaching a Diffusion Pump to a Vacuum System
- •7.3.14 How to Use a Diffusion Pump
- •7.3.15 Diffusion Pump Limitations
- •7.3.17 Diffusion Pump Maintenance
- •7.3.18 Toepler Pumps
- •7.4 Traps
- •7.4.1 The Purpose and Functions of Traps
- •7.4.2 Types of Traps
- •7.4.3 Proper Use of Cold Traps
- •7.4.4 Maintenance of Cold Traps
- •7.4.5 Separation Traps
- •7.4.6 Liquid Traps
- •7.5 Vacuum Gauges
- •7.5.2 The Mechanical Gauge Family
- •7.5.4 The Liquid Gauge Family
- •7.5.5 The Manometer
- •7.5.6 The McLeod Gauge
- •7.5.7 How to Read a McLeod Gauge
- •7.5.8 Bringing a McLeod Gauge to Vacuum Conditions
- •7.5.10 The Tipping McLeod Gauge
- •7.5.11 Condensable Vapors and the McLeod Gauge
- •7.5.12 Mercury Contamination from McLeod Gauges
- •7.5.13 Cleaning a McLeod Gauge
- •7.5.14 Thermocouple and Pirani Gauges
- •7.5.15 The Pirani Gauge
- •7.5.16 Cleaning Pirani Gauges
- •7.5.17 The Thermocouple Gauge
- •7.5.18 Cleaning Thermocouple Gauges
- •7.5.19 The lonization Gauge Family
- •7.5.20 The Hot-Cathode Ion Gauge
- •7.5.21 Cleaning Hot-Cathode Ion Gauges
- •7.5.24 The Momentum Transfer Gauge (MTG)
- •7.6 Leak Detection and Location
- •7.6.1 AllAbout Leaks
- •7.6.3 False Leaks
- •7.6.4 Real Leaks
- •7.6.5 Isolation to Find Leaks
- •7.6.6 Probe Gases and Liquids
- •7.6.7 The Tesla Coil
- •7.6.8 Soap Bubbles
- •7.6.9 Pirani or Thermocouple Gauges
- •7.6.10 Helium Leak Detection
- •7.6.11 Helium Leak Detection Techniques
- •7.6.13 Repairing Leaks
- •7.7 More Vacuum System Information
- •7.7.1 The Designs of Things
- •8 The Gas-Oxygen Torch
- •8.1.2 How to Light a Gas-Oxygen Torch
- •8.1.3 How to Prevent a Premix Torch from Popping
- •8.2.2 How to Tip-Off a Sample
- •8.2.3 How to Fire-Polish the End of a Glass Tube
- •8.2.4 Brazing and Silver Soldering
- •Appendix
- •A.2 Suggestions for Glassware Requests
- •B.1 Introduction
- •B.2 Polyolefins
- •B.3 Engineering Resins
- •B.4 Fluorocarbons
- •B.5 Chemical Resistance Chart
- •C.1 Chapter 1
- •C.4 Chapter 4
- •C.5 Chapter 5 & Chapter 6
- •C.6 Chapter 7
- •C.7 Chapter 8
- •D.1 Laboratory Safety
- •D.2 Chemical Safety
- •D.3 Chapter 1
- •D.4 Chapter 2
- •D.5 Chapter 3
- •D.6 Chapter 4
- •D.7 Chapter 5 and the Second Half of Chapter 6
- •D.8 Chapter 7
- •D.9 Chapter 8
- •Index
The Regulator 5.2 |
283 |
5.2.4 How to Use Regulators Safely
Always open the main tank valve slowly. Intense pressure against the regulator's diaphragm can cause premature wear and aging. In addition, after the main tank valve has been turned off, the regulator should not remain under pressure for extended periods of time (i.e., several hours or beyond). The procedure of closing the tank valve (V-l; see Fig. 5.4) and then bleeding the system to release any remaining gases will help extend the life of the regulator. This bleeding procedure is more critical with two-stage regulators which may trap a small quantity of gas within the first of their two stages. This gas can then burst out unpredictably and potentially dangerously.
Another practice for extending the life of a regulator is to unscrew (CCW) the pressure adjusting valve (V-2; see Fig. 5.4) before opening the tank valve (V-l; see Fig. 5.4) and before setting the regulator to the desired pressure. In addition, open the tank valve slowly to limit the amount of shock on the diaphragm. Continued shock on the diaphragm causes premature aging.
When opening the main tank valve to allow gas into the regulator, you should stand to the side (not in front or behind) of the gauges, preferably with the main tank valve between you and the regulator. If an old worn diaphragm bursts during the sudden pressure increase, glass and metal shards could spray out. This damage cannot happen if the pressure adjusting valve is unscrewed before you open the main valve because there is no pressure against the diaphragm.
Never use oil in or around a regulator. Oxygen regulators (CGA fitting 540) pose special dangers because oxygen decreases the ignition temperature of flammable materials. Oil around compressed oxygen can explode. Do not use plumbing "pipe dope" on a CGA fitting. If a CGA fitting needs "pipe dope," there is something wrong with the fitting and it should not be used.
Do not use a regulator that has been dropped or shows any signs of physical abuse. If in doubt, have the regulator checked at the manufacturer's service center.
When storing a regulator, place it in a plastic bag to prevent dirt and dust from settling on, and in, the regulator. Dust and dirt can damage the diaphragm, or wedge within the sections, preventing complete closing of the diaphragm parts. Regulator cleaning and repair should be done by a service agency and should not be done by inexperienced personnel.
5.2.5 How to Test for Leaks in a Compressed Gas System
The first leak to check is within the regulator: To see if there is gas leakage past the diaphragm, rotate the pressure adjusting valve CCW until it is fully open, then slowly open the main tank valve. If any gas leaves the regulator, the regulator is defective or broken and needs repair or replacement.
To see if you have a leak within the line of your pressure system, close all normal outlets. Then, after opening the main tank valve and rotating the pressure adjusting valve (V-2; see Fig. 5.4) to the desired pressure, turn the main tank valve
284 Compressed Gases
off. If you see a dropping off of pressure on the tank pressure gauge, you have a leak somewhere in your system.
To limit the region needing examination, rotate the pressure adjusting valve CCW one or two revolutions. If the reading on the tank pressure gauge drops, there is a leak in the compressed tank valve, the CGA fitting, or the tank pressure gauge. However, if the outgoing pressure gauge drops, there is a leaky outlet fitting, needle valve (if any), outgoing pressure gauge, hose, tubing leaving the regulator, or any other part of the system beyond the regulator. Finally, if the tank pressure gauge drops and the outgoing pressure gauge rises, there is a leak in the regulator itself. (It is normal to see this last pressure rise when you are bleeding the pressure from a single-stage regulator just as the pressure in the regulator is almost extinguished.)
If you know you have a leak but are not sure of the location, do not use a flame to aid your search.* If the gas is flammable, the dangers are obvious, but otherwise there is concern of burning parts and equipment. The best and safest technique is to spray, squirt, or drip a soapy water solution on the suspected area. Use either a diluted liquid dish soapf or a commercial solution such as Snoop®.* The evidence of bubbles is a sure sign of a leak. However, be sure you witness bubble formation as opposed to bubbles just sitting there, which are likely to have formed during the application of the bubble solution.
5.2.6 How to Purchase a Regulator
Most regulators can provide uniform and accurate high-pressure output. Where regulators vary is in their output potential. A large gas demand requires a regulator with a large output potential. By selecting a regulator that only satisfies the minimum flow rate for your expected needs, you may be unable to achieve unexpected high-flow demands.
A wailing noise coming from your regulator is a symptom of using a large quantity of gas at a rate faster than the diaphragm within the regulator is capable of supplying. Unless you are able to use a smaller quantity of gas, the best solution is to purchase a larger regulator with a higher flow capacity (typically a twostage regulator) and/or a better quality regulator.
If you absolutely need constant outgoing pressure, regardless of varying tank pressure or the varying rate of outgoing gases, select a two-stage regulator; otherwise, a single-stage regulator is sufficient. Although the changes are subtle, sin- gle-stage regulators have less stable outgoing pressures as tank pressure drops or as you increase the rate of outgoing gases.
If you are using a corrosive gas, it is imperative to use a stainless steel regulator. Otherwise, a brass regulator is sufficient.
Some people use the flickering of a flame as an indication of a leak.
+Liquid dish soap can corrode stainless steel, so rinse it off when completed. *SNOOP®, Product of the Nupro® Company, Willoughby, OH 44094.
The Regulator 5.2 |
285 |
When you order a regulator, expect to receive only the regulator. Unless you specify that you also want a needle valve and/or a barb (hose connection), you probably will not get one! Be sure to ask the salesperson what you will be receiving with the regulator. This information becomes more important if you are ordering a regulator for a tank that has a left-handed CGA fitting such as a propane tank, because all the fittings for this regulator will also left-handed. If you wish to add a hose connection onto the regulator after it has arrived at your lab, you might end up digging through drawers filled with right-handed fittings and no luck in finding a left-handed hose connection. If this happens, you may have to go back to your mail-order supplier or to a local welding supply house.