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can be used to determine leaks in casing, tubing or the packer, and
will also be used for lift gas injection into the casing.
The tubing hanger (also called donut) is used to position
the tubing correctly in the well. Sealing also allows Christmas tree
removal with pressure in the casing.
Master gate valve. The master gate valve is a high quality
valve. It will provide full opening, which means that it opens to the
same inside diameter as the tubing so that specialized tools may be
run through it. It must be capable of holding the full pressure of
the well safely for all anticipated purposes. This valve is usually
left fully open and is not used to control flow.
The pressure gauge. The minimum instrumentation is a
pressure gauge placed above the master gate valve before the wing
valve. In addition other instruments such as temperature will
normally be fitted.
The wing valve. The wing valve can be a gate valve, or
ball valve. When shutting in the well, the wing gate or valve is
normally used so that the tubing pressure can be easily read.
The swab valve. The swab valve is used to gain access to
the well for wireline operations, intervention and other workover
procedures (see below), on top of it is a tree adapter and cap that
will mate with various equipment.
The variable flow choke valve. The variable flow choke
valve is typically a large needle valve. Its calibrated opening is
adjustable in 1/64 inch increments (called beans). High-quality
steel is used in order to withstand the high-speed flow of abrasive
materials that pass through the choke, usually for many years, with
little damage except to the dart or seat. If a variable choke is not
required, a less expensive positive choke is normally installed on
smaller wells. This has a built in restriction that limits flow when
the wing valve is fully open.
This is a vertical tree. Christmas trees can also be
horizontal, where the master, wing and choke is on a horizontal
axis. This reduces the height and may allow easier intervention.
Horizontal trees are especially used on subsea wells.

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