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Building 510C

P.O. Box 5000

Upton, NY 11973-5000

Phone 516 344-6102

Fax 516 344-3253

sivertz@bnl.gov

managed by Brookhaven Science Associates\
for the U.S. Department of Energy

*date: July 27, 2001*

*to: Yousef Makdisi*

*from: Michael Sivertz*

*subject: PHENIX Drift Chamber gas piping modifications*

This note gives the plan for adding a pair of gas pipes to the existing
DC/PC gas system to allow for separate controls of the DC Gas System in
the Gas Mixing House (GMH).

**Motivation**:

Currently the DC/PC Gas System uses a single pipe to bring the
Argon/Ethane 50/50 gas mixture from the GMH to the IR where the pipes to
the East Carriage and West Carriage are separated. The final division
between DC and PC is accomplished in the Carriage Racks.

The DC group would like to allow for bubbling the DC operating gas
through alcohol or water, while the PC group does not want to have
alcohol or water in its operating gas. In order to allow for different
gas mixtures, the DC and PC gas pipes must be separated in the GMH.

A pair of flexible stainless steel pipes was run from the GMH to the IR.
One pipe would be used for each DC on the East or West Carriage. The
pipes are 3/4\" in diameter. These would replace the 1.5\" diameter pipe
now being used for both the DC and PC. The existing pipe would be used
solely by the PC.

Future gas system modifications involving the addition of a bubbler, new
pressure regulators and pressure transducers will be addressed in
another review at a future date.

**Safety Precautions:**

All High Voltage to the DC and PC shall be turned off before beginning
this work.

All subsequent work in the IR and GMH will be monitored with the use of
a flammable gas sensor to ensure that there is no flammable gas present
during the work. The PHENIX flammable gas safety system will be
operational in the GMH and IR throughout the duration of this work.

**Inerting the gas pipes:**

In order to connect the new pipes, the existing pipes must be purged of
flammable gas before cutting into them. The volume of the pipes is less
than 2.5 cubic feet (CF). Flowing at a rate of 40 cubic feet per hour
gives a complete exchange of gas every six minutes, or eight exchanges
in 50 minutes. The inert gas would be allowed to flow into the DC and
PC, effectively purging the pipes into the chambers. After eight
exchanges the gas in the pipes will be non-flammable. Solenoid valves in
the Carriage Racks will be closed sealing off the East and West DC and
PC. Solenoid valves in the GMH will be closed stopping the gas flow. At
this point it is safe to work on the gas pipes.

**Modifications in the GMH:**

We will cut into the gas supply piping in the DC/PC Gas Rack in the GMH.
Existing connections will be cut using pipe cutters. A junction will be
added allowing the new DC pipes to be connected. A single pipe will
bring the gas from the existing DC/PC Rack in the GMH to a new DC
Bubbler Rack, also in the GMH. There the gas pipe will be divided again
to allow for separate control of the East and West DC gas supplies. The
gas pressure will be regulated separately as well with the addition of
three new regulators. A four-way valve in each of the East and West DC
gas pipes will allow for the addition of a pair of bubblers in the
future. All new connections will be made with Swagelok fittings making
cleaning of the pipes unnecessary.

**Modifications in the IR**:

In the IR, there are separate flow meters in the Carriage Racks for the
DC and PC. The existing pipe supplying these flow meters will be
replaced by a pair of pipes; one coming from the new flexible stainless
steel pipe, and one from the end of the existing pipe. All connections
will be made with 3/4\" Swagelok fittings.

**Restarting flammable gas flow**:

Before starting to flow flammable gas, it is important to flash the new
pipes with inert gas to assure that no oxygen will be introduced into
the DC or PC. We will begin flowing inert gas to the new and old pipes
by opening up the solenoid valves in the GMH. The new pipe connections
to the Carriage Gas Racks will be left loose so that the inert gas leaks
out at the carriages. The air in the pipes will be flushed into the IR
in this process. Flowing at a rate of 40 SCFH, we will have purged the
pipes of oxygen in 50 minutes. At that time the connections at the
Carriage Gas Racks will be made gas tight. Then the solenoid valves to
the DC and PC detectors will be opened and we will begin flowing
operating gas again.

All new gas connections will be checked with a flammable gas detector to
assure that there are no leaks in the new or old piping.