1 saw 1.1 \documentclass{chowto}
2
3 \title{Drift Chamber Gas System Operation}
4 \howtotype{expert} % ``expert'', ``user'', ``reference''
5 %\experiment{Name of experiment} % Optional
6 \author{H. Fenker}
7 \category{general} % Subject area of this document
8
9 %\maintainer{Name of person maintaining document} % Optional
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10 saw 1.2 \date{April 4, 2003} % Can use \today as the argument
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11 saw 1.1
12
13 \begin{document}
14 \providecommand{\degg}{\ensuremath{^{\circ}\ }}
15
16 \begin{abstract}
17 This document provides detailed setup information for the drift chamber gas mixing
18 system, as well as the correct procedure for refilling the alcohol supply and changing
19 gas bottles. This information is intended for use by {\bf gas system experts only.}
20 For day-to-day shift worker instructions, refer to the corresponding {\it user} howto
21 document.
22 \end{abstract}
23
24 \section{Overview}
25
26
27 The drift chamber gas is composed of 50\% Argon and 50\% Ethane (by volume),
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28 saw 1.2 bubbled through isopropanol at 1\degg C. This results in gas containing
29 approximately 1\% alcohol vapor. The mixing system that produces this
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30 saw 1.1 gas is housed in the gas shed. The bottles supplying the gas to the mixing
31 system are attached to two two-bottle manifolds outside the gas shed, within
32 the fenced-in gas bottle yard.
33
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34 saw 1.2 \section{Gas Interlock System}
35 The flow of gas from the supply bottles may be automatically shut off by
36 normally-closed solenoid valves installed in the primary argon and ethane manifolds. Several
37 conditions such as overtemperature, fan failure, gas leak, and fire alarm must all
38 be in the non-alarm state before these valves will open. Alarm conditions are
39 indicated on the gas system alarm panel on the lower-left side of the
40 center counting-house console.
41
42 When any of the required conditions is not satisfied the sounder on the panel
43 will make an annoying noise and both solenoid valves will close. The audible
44 alarm may be silenced by a toggle switch on the panel. Be certain to return
45 it to the ``on'' position as soon as the fault is cleared.
46
47 The most confusing, but most common alarm condition is ``Low Pressure''.
48 The solenoid valves will not remain open unless there is already ample pressure
49 on the output side of both valves. This prevents us from flowing, for example,
50 pure ethane to the drift chambers when the argon bottle is empty. The way
51 to clear this condition is to make sure there are no other faults and that
52 both argon and ethane manifolds are properly pressurized and fitted with
53 non-empty bottles; then press and hold the ``override'' button for several
54 seconds. This button forces the solenoid valves to open even if there are
55 saw 1.2 fault conditions present. If all is well, gas will flow through the valves
56 and clear the ``low pressure'' condition so that the button many be released.
57
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58 saw 1.1 \section{Settings for Normal Operation}
59
60 Refer to the gas system flow diagram, Fig. \ref{fig:gas_mixer_diagram}
61 \begin{figure}
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62 saw 1.2 \psfig{figure=drift_gas_system-mixer_diagram.eps,width=6in,bbllx=12,bblly=12,bburx=750,bbury=590}
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63 saw 1.1 \caption{Diagram of Hall~C Gas Mixing System\label{fig:gas_mixer_diagram}}
64 \end{figure}
65
66
67 For normal operation, with the alcohol systems in use, the valves
68 should be set as follows:
69
70 {\bf For The HMS:}
71
72 Open - 3, 4, 11, 14; Closed - 12, 13, 17, 18, 19, 20.
73
74 The nominal flows set in the mass flow controller are:
75 \begin{itemize}
76 \item Channel 3 (Argon): 0.3~slpm (standard liters per minute)
77 \item Channel 4 (Ethane): 0.3~slpm
78 \end{itemize}
79
80
81 Unless the gas \#3 Mass flow control valve is installed, valve \#6 should
82 always be closed.
83
84 saw 1.1 {\bf For the SOS:}
85
86 Open - 1, 2, 7, 10; Closed - 8, 9, 15, 16, 19, 21.
87 \begin{itemize}
88 \item Channel 1 (Argon): 0.15~slpm
89 \item Channel 2 (Ethane): 0.15~slpm
90 \end{itemize}
91
92
93 Unless the gas \#3 Mass flow control valve is installed, valve \#5 should
94 always be closed.
95
96 \section{Operating the Mass Flow Controller.}
97
98 The gas flow is controlled by a MKS 647 controller and mass flow
99 control valves. The 647 is menu driven from a CRT in the front panel and
100 with a keypad with cursor controls. The 647 features a non-volatile memory
101 so settings are retained even if the unit is unpowered. The initial menu
102 upon startup is the Command Menu. For normal operation use either the User
103 Display menu (Command menu item \#1) or the Extended Display menu (Command
104 menu item \#2). The User Display menu shows actual flow in each channel and
105 saw 1.1 the total flow in all channels. The Extended Display menu shows actual
106 flow, flow set point, units, valve full scale range, gas calibration
107 factor, whether that channel is enabled, and whether each channel is
108 operating in master, slave, or independent mode.
109
110 \subsection{To set flow rates:}
111
112 The flow rate set points are adjusted from the Extended Display
113 menu. There are two methods to change valve flow rate set point. If you
114 want to enter a specific value you must first turn off the flow in that
115 channel or all of the channels. Using the cursor keys move the cursor to
116 the desired channel. Enter the desired flow rate.
117
118 The flow rate set point can be changed with gas flowing using the
119 cursor keys. In the Extended Display mode move the cursor to the desired
120 channel using the left/right cursor keys. The set point can then be
121 adjusted up or down using the cursor up/down keys.
122
123 \subsection{To turn gas flow on or off:}
124
125 The gas flow can be turned on or off while in any menu. When any
126 saw 1.1 of the mass flow valves are open the green LED labeled ``GAS ON" on the 647
127 is lit. When none of the gas flow valves are open the red ``STAND BY" LED
128 will be flashing. In the Extended Display menu the bottom line displays on
129 or off, by channel, to show which mass flow valves are enabled. The green
130 LED must be lit and an ``ON" must be displayed in the bottom row of the
131 Extended Display menu for gas to be flowing in a particular channel.
132
133 {\bf Turning the gas on or off is done in two steps which can be done in
134 either order.}
135 Each channel must be enabled by pressing ``ON" and then
136 that channel number. The command input must be enabled by pressing ``ON"
137 and then ``ALL" from the keypad. This allows a single channel or all of the
138 enabled channels to be turned on or off at once. Both steps must be
139 performed initially, but thereafter only one of the steps need be performed
140 to cycle the gas flow on or off.
141
142 To turn gas off in a single channel press ``OFF" and then the
143 desired channel. If you want to close all the valves simultaneously, press
144 the ``OFF" key and then the ``ALL/0" key. To turn gas back on you must
145 reverse whichever sequence you used to stop the gas flow. For example if
146 you turned the gas off by pressing ``OFF" and then the channel number, it
147 saw 1.1 must be turned back on by pressing ``on" and then the channel number. If
148 you turn off all the channels by pressing ``OFF" , ``ALL" you must turn it
149 back on by pressing ``ON" , ``ALL."
150
151 \section{To Change a Gas Bottle}
152
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153 saw 1.2 The argon and ethane supply bottles should be replaced by new (full)
154 bottles when the bottle content drops below about 10\% of its capacity.
155 For argon, the bottle content is directly indicated by the bottle
156 pressure: a new bottle usually contains 2000 to 3000~psig. Argon bottles
157 should be changed whenever the bottle pressure is found to be below
158 about 200~psig. Ethane bottles, on the other hand, contain liquified
159 ethane. Thus the bottle pressure is just the vapor pressure of ethane
160 at whatever the current temperature happens to be. At 70\degg F this is
161 about 544~psig. The pressure guage
162 will not tell you how much ethane is left in the bottle until it
163 reads zero! Instead, we measure the ethane content by observing the
164 weight of the bottle and comparing it to the weight when the bottle
165 was full. A standard B-size cylinder contains about 32~pounds of ethane.
166 Thus, when the bottle weight is about 30~pounds less than its full weight,
167 the bottle should be replaced. Recent (as of April 2003) experience
168 indicates that full bottles weigh $165\pm 1 lbs.$
169
170 Handling and connecting bottles of compressed gas require special knowledge.
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171 saw 1.1 The high pressure gas stored in the cylinders (bottles) constitutes significant
172 stored energy. Mishandling of a gas bottle can pose a lethal hazard! Refer to
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173 saw 1.2 the JLab EH\&S Manual\cite{bi:jlabehs} for safe handling practices. If you do not already know
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174 saw 1.1 how to safely manipulate compressed gas hardware, have a knowledgeable
175 person train you.
176
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177 saw 1.2 \section{To by-pass the alcohol system}
178
179 \noindent For the HMS:\\
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180 saw 1.1 Open valves 12 \& 13, then close valves 11 \& 14, in that order!
181
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182 saw 1.2 \noindent For the SOS:\\
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183 saw 1.1 Open valves 8 \& 9, then close valves 7 \& 10, in that order!
184
185 \section{The Alcohol Bubblers}
186
187 To reduce the rate of aging of the wire chambers, the operating gas contains
188 a small quantity of alcohol vapor. The vapor is added by bubbling the argon/ethane
189 mixture through liquid alcohol. The temperature of the alcohol controls the
190 alcohol vapor pressure, which determines the
191 amount of vapor added to the gas. The alcohol content also affects the
192 electron dirft velocity in the wire chambers, so it must be held
193 approximately constant.
194
195 \subsection{To refill the alcohol bubblers:}
196
197 The alcohol bubbler system features a refill system that allows
198 filling directly from the bottle, minimizing exposure of the alcohol to air
199 and reducing the possibility of a spill.
200 {\bf The reservoirs should be refilled
201 before they become empty to maintain a head of liquid over the float valve
202 which will prevent air from entering the system.}
203 In the back of the gas
204 saw 1.1 system rack is a holder for gallon sized alcohol bottles and a cap with dip
205 tube. Place a new bottle in the bottle holder and replace the cap with the
206 cap with dip tube.
207
208 \subsection{Step-by-Step Instructions for Refilling the SOS Alcohol Bubbler}
209 \em{These steps must be individually completed in the order listed!}\\
210 Refer to Fig.~\ref{fig:gas_mixer_diagram}.
211 \begin{enumerate}
212 \item{If needed, install a full bottle of alcohol in the back of the gas racks as mentioned in the preceeding paragraph.}
213 \item{{\em Open valves 8,9. Close valves 7,10} to Put the SOS alcohol bubbler in BYPASS.}
214 \item{{\em Close valve 16} to isolate the warm reservoir gas from the bubbler.}
215 \item{{\em Open valve 15} to bleed off the warm reservoir gas pressure.}
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216 saw 1.2 \item{Certify that the pressure feeding valve 19 is 1 psi or less so that you
217 do not cause the alcohol bottle to explode when you pressurize it. {\em Wear
218 safety glasses!!}}
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219 saw 1.1 \item{{\em Open valve 19} to pressurize the alcohol bottle.}
220 \item{{\em Open valve 21} to flow alcohol into the warm reservoir.}
221 \item{When the alcohol level in the sight-glass is within 2cm of the top, stop
222 the flow of alcohol: {\em Close valve 21.}}
223 \item{{\em Close valve 19.}}
224 \item{{\em Open valve 16.}}
225 \item{{\em Close valve 15.}}
226 \item{{\em Open Valves 7 and 10. Close Valves 8 and 9.}}
227 \item{Record what you did in both the gas logbook and the electronic logbook.}
228 \end{enumerate}
229
230 \subsection{Step-by-Step Instructions for Refilling the HMS Alcohol Bubbler}
231 \em{These steps must be individually completed in the order listed!}\\
232 Refer to Fig.~\ref{fig:gas_mixer_diagram}.
233 \begin{enumerate}
234 \item{If needed, install a full bottle of alcohol in the back of the gas racks as mentioned in the preceeding paragraph.}
235 \item{ {\em Open valves 12,13. Close valves 11,14} to Put the HMS alcohol bubbler in BYPASS.}
236 \item{{\em Close valve 18} to isolate the warm reservoir gas from the bubbler.}
237 \item{{\em Open valve 17} to bleed off the warm reservoir gas pressure.}
238 \item{{\em Open valve 19} to pressurize the alcohol bottle.}
239 \item{{\em Open valve 20} to flow alcohol into the warm reservoir.}
240 saw 1.1 \item{When the alcohol level in the sight-glass is within 2cm of the top, stop
241 the flow of alcohol: {\em Close valve 20.}}
242 \item{{\em Close valve 19.}}
243 \item{{\em Open valve 18.}}
244 \item{{\em Close valve 17.}}
245 \item{{\em Open Valves 11 and 14. Close Valves 12 and 13.}}
246 \item{Record what you did in both the gas logbook and the electronic logbook.}
247 \end{enumerate}
248
249 \subsection {Alcohol Temperature Control}
250
251 To keep the alcohol temperature (and thus the vapor pressure) constant,
252 the alcohol bubblers are housed in refrigerators which are controlled by
253 electronic temperature regulators having 1~C\degg sensitivity. Both
254 controllers are located on a shelf in the left rack of the gas mixing
255 system. Normally, the actual temperature in each refrigerator is
256 indicated on the front panel of the controller. Both controllers should
257 be set to maintain a temperature of 1\degg C.
258
259 \section{Gas Filters Maintenance}
260
261 saw 1.1 There are gas filters on the argon and ethane supply lines just inside
262 the gas shed. These filters should be replaced on a regular schedule.
263 See Bill Vulcan for details.
264
265 \section{Secure Pressure Regulators}
266
267 The gas mixing system is protected from failure or mis-setting of the
268 primary pressure regulators (the ones mounted on the manifolds on the
269 exterior of the gas shed -- near the bottles) by {\it hidden} regulators
270 mounted just inside the gas shed. It is these regulators which actually
271 set the maximum supply pressure to the mixing valves. These regulators
272 should {\em never} be adjusted by other than a gas system expert! The
273 nominal secondary pressure supplied by both the argon and ethane
274 secure regulators is 15 psig.
275
276
277 \section{Related {\it Howtos}}
278 \begin{itemize}
279 \item MKS 647 Mass Flow Controller Howto \cite{howto:MKS_controller_TM}
280 \item Flammable Gas Detector System \cite{howto:flam_gas_detector}
281 \item Gas System Interlock Panel \cite{howto:gas_interlock_panel}
282 saw 1.1 \item Base Equipment Shift Checklist Items \cite{howto:base_equip_checklist}
283 \end{itemize}
284
285 \end{document}
286
287 % Revision history:
288 % 1st draft by Howard Fenker 27FEB03 -- taken from existing ops manual.
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289 saw 1.2 % $Log: drift_gas_system.tex,v $
290 % Revision 1.1 2003/03/03 20:08:14 saw
291 % Initial Checkin
292 %
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