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GARRETT VALVE
Garrett oil tools produced their first valve in 1946.
The model numbers include: D, D-1, D-2, D-3, E, and ED.
Parts are still available for these valves and we can assist you with
identifying the proper replacement parts by calling Toll Free - 877-244-4884.
Note: Please do your best to provide the valve's serial number. |  |
In
most installations of this type, air is required to start the main compressor engines and with this available source of pressure the air is usually used to operate various control instruments; therefore, we are using the same low-pressure air to operate all valves. Operators for higher pressures are available. See Diagram
We will assume that the air compressors are such to produce a pressure of 250 psig. Instrument air systems only require 30-40
psig pressures and some instruments require much less; therefore, for example, let's control the shown air lines to 40 psig and set the "E0-3" operators to 30 psig. By doing this, if we open an emergency shutdown valve (valves 15, 16, or 17), we could drop our 40-psig-air system to 30 psig and open valves 5, 4, 7, 9 and close valves 1 and 3.
To ascertain that air pressures does not get above 250 psig due to some malfunction, it is necessary that (valve 10) a Garrett
Relief Valve Type D-3 be installed and set to relieve at 250 psig. Code regulations also require relief valve on the air receivers.
To control the air system to 40 psig, we recommend our DCB-1 motor valve with a "YL" control be installed with a flow bean or choke downstream (see
detail A). To put the system in operation, simply open the by-pass valve, and the DCB-1 motor valve will take over and control the pressure. The Flow Bean or Choke assures that the maximum flow cannot enter the system during an emergency.
The system shown is a pressure reducing system; however, the system can have the same simplicity in a pressure increasing system or an electrical solenoid operated system.
"E0-3" Relief Valve Operator
The operator is attached to the relief valve by installing bracket (Index 31) under one bonnet bolt. The pressure connection is made to the relief valve through the manual blowdown valve or through an additional tapped hole in the bonnet to the flexible hose (index 34). The control pressure is applied through flexible hose (index 37). Pull out locking pin (index 24), before applying operator pressure (10# to 85#). This pressure is effective on the 3-1/2" diameter piston (9.6
sq. inches), which keeps the operator closed against the opposing force, which is the pressure on the relief valve 3/8" diameter (.11 sq. inches).
The designed opening pressure of the operator is set by adjusting nut (index 3). Turn adjusting nut clockwise to open operator at a higher control pressure or counter clockwise to open at a lower control pressure.
By venting the control pressure to atmosphere to the desired
opening pressure, the pressure from the relief valve bonnet plus the force of the spring opens the operator. thus venting the relief valve bonnet valve to open, thereby venting the system on which the relief valve is installed to atmosphere and remains open until the operator is manually unlocked and control pressure restored.
System Operation
Assume an air control pressure of 40 psig and an emergency occurs; all that is necessary is to open valve 15, 16 or 17 (Note: additional valves can be installed at any particular location desired for emergency blowdown.) At which time the following occurs to each valve:
Valve No.- 1 Suction Fire Gate Closes
- 3 Discharge Fire Gate Closes
- 4 Suction Relief Valve Opens
- 5 Discharge Relief Valve Opens
- 7 Compressor Unit Relief Valves Open
- 9 Fuel Gas Relief Valve Opens
It is readily noted that by closing the suction and discharge fire gates the entire compressor station is isolated from the
main line.
Normal designs and codes require that a relief valve be installed inside the discharge fire gate (valve #5) if a pneumatic operator is installed on the discharge fire gate.
It is utterly necessary that each compressor unit discharge be equipped with a relief valve (valve #7) in order to protect a multi-thousand dollar compressor unit in case of any over pressure.
The fuel gas relief valve (valve #9) is very necessary in case a regulator cuts out and allows suction pressure into the fuel system of each engine.
Agreed that the above is required, then for only a fractional
amount of monies for "E0-3" operators, each of these valves can become a blowdown valve and be actuated separately from the relief function.
The Garrett Relief Valve (valve #4) shown inside the suction fire gate becomes a balance valve for specific blowdown time. Codes require relief valves on pressure vessels, and even though not shown, the Garrett Relief Valves (valves #6) could be tied into the same system and speed up blowdown time.
Testing
Any emergency shutdown system becomes worthless if the design is such that testing is hard to accomplish or you just lose thousands of dollars of gas to perform a single test.
Valves 12, 13, and 14 are small isolation valves. Note that under Garrett Relief Valves 4, 5, and 9 a block valve is installed.
To check the system in operation, close the block valve under Garrett Relief Valves 4, 5, and 9. Close isolation valves 12, 13, and 14. Open an emergency shutdown valve (No. 15, 16 or 17)
and the three valves 4, 5, and 9 will open and the station will continue to operate. To put system back into operation, refer to "E0-3" Relief Valve Operator Section. After air system is back in operation, open valves 12, 13, 14 and the entire
system is back in operation. The pneumatic operators on valves 1 and 3 can be checked approximately one half turn before restricting flows, and with every manufacture's pneumatic operator, this test can be performed. In this procedure we did
not check (valves #7) on each compressor unit discharge; however, in most cases the size of the orifice within the valves has very little effect on blowdown time.
All Garrett Relief Valves, regardless of location, have a fourfold purpose: - Relief Function
- Blowdown Function
- When used as a blowdown valve the system does not require purging as the Garrett relief Valve Piston weight is such to trap 1 - 2# gas pressure.
- Split piston serves as check valve on backpressure.
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