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

 10 saw   1.2 \date{April 4, 2003} % Can use \today as the argument

 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),

 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

 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           

 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           

 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}

 62 saw   1.2 \psfig{figure=drift_gas_system-mixer_diagram.eps,width=6in,bbllx=12,bblly=12,bburx=750,bbury=590}

 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           

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.

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

173 saw   1.2 the JLab EH\&S Manual\cite{bi:jlabehs} for safe handling practices. If you do not already know

174 saw   1.1 how to safely manipulate compressed gas hardware, have a knowledgeable
175           person train you.
176           

177 saw   1.2 \section{To by-pass the alcohol system}
178           
179           \noindent For the HMS:\\

180 saw   1.1 Open valves 12 \& 13, then close valves 11 \& 14, in that order!
181           

182 saw   1.2 \noindent For the SOS:\\

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.}

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!!}}

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.

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           %