Refurbishment Instructions¶

In the first steps of refubishment you must first print out the test paperwork and validate the information on the cold head label, repair tag, and paperwork.

Definitions¶

There are many interchangeable words that refer to components within the cold head. Below are the standardized versions although some words may be used interchangably.

Cold Head
An alternative term for cryocooler. The cryocoolers referred to in this document are GM type cryocoolers.

Housing Assembly
The housing assembly refers to the complete mechanical drive mechanism outside the cylinder. This is the central aluminmum housing with scotch yoke guide bushing installed, motor, valve body assembly, upper cup assembly, and scotch yoke.

Motor Assembly
The motor assembly refers to the cold head motor complete with power receiptical, crank, and crank bushing.

Displacer Regenerator Assembly

The displacer regenerator assembly refers to the displacer set inside the cylinder.

Cylinder
The cylinder is the long portion of the cold head that the displacer-regeneration assembly is driven. The first and second stage heat stations are located on the cylinder and it bolts to the cold head housing.

PROCEDURE¶

Visual Inspection¶

Visually Inspect the cold head, and make note of any dents, missing parts, or other damage. The aluminum housings on cold heads are suseptable to denting from tools and mistreatment. The cylinders are also suseptable to bending and denting. It can be difficult to notice a bent cylinder but if there is any evidence of an impact to the second stage then there is a greater chance the cylinder is bent.

The A2 is also equipped with a sensor in the second stage. This sensor has a wire that wraps around the entire cold head cylinder and meets a hermetically sealed Detoronics connector at the transition flange. This wire is extremely thin and suseptable to scrathing, bumps, and shorting. Inspect this wire for any evidence of damage.

When cold heads come back from the field they tend to have significant evidence of the previous installation. This will include indium metal, o-rings, tape, and vacuum grease.

Clean the Transition Flange Gland¶

Remove the o-ring by pinching the o-ring in any spot. This creates a loop to grab the oring by.

Use a dry papertowel to clean up any large gobs of vacuum grease around the transition flange.

Use a kim wipe to clean up any residual vacuum grease on or in the o-ring gland

Use a kim wipe with alcohol to clean off the o-ring

Apply a thin layer of vacuum grease to the o-ring and re-install it

Remove any indium, tape, or residual glue from the cylinder.

Place the cold head into the cold head repair cart.

Tear Down¶

Danger

The remainder of this procedure should be performed with nitrile gloves, safety glasses, and breathing mask on. Fine dust is unsafe to breathe and tastes bad. The displacers should also remain dry and the oils from your hands will soak into the phenolic linen.

Connect the discharge valve and gauge to the return aeroquip on the cold head.

Apply drive power to the cold head an record the pressure readout of the gauge.

Record any sounds that the cold head is making.

Discharge the helium.¶

While driving the cold head motor open the valve on the discharge valve and gauge to release the pressure from the cold head. Allow the cold to cycle 3 or more times with the valve open to ensure the pressure is equalizes.

Remove the discharge vlave and gauge. Then loosen and remove the four M8 bolts holding the houseing down to the cylinder.

Lift the cold head with the displacer-regenerator assembly free from the cylinder.

Displacer orientation¶

Record the orientation of the first stage displacer¶

Lay the cold head housing assebmly with the regenerator displacer assembly attached on its side. Position the regenerator displacer assembly to the right, the cold head housing assembly to the left, and the aeroquips pointing away.

There are three options per A and B direction.

A is the up direction with the fastener at the most zenith point is set away from you with the cold head housing assembly to your left and the displacer-regenerator assembly to your left

R1A
R2A
R3A

B is the down direction with the fastener at the most zenith point is set closer to you with the cold head housing and the displacer-regenerator assembly in the same configuration

R1B
R2B
R3B

Record the orientation of the second stage displacer¶

There are two options per direction, U and D.

U is the up direction of the "S" stamp located on the bottom of the displacer in relationship to the horizontal plane the first stage pin creates when in the 1^st position.

SUA
SUB

D is the down direction of the "S" stamp located on the bottom of the displacer in relationship to the horizontal plane the first stage pin creates when in the 1^st position.

SDA
SDB

Displacer processing¶

Separate the second stage displacer by removing the pin holding the first and second stage displacers together.

Save the the pin and note the number of triple wave washers instaled as well as any shims.

Remove the three M6 fasteners on the the first stage displacer and separate it from the mounting plate.

Record the serial numbers of both the first stage and the second stage displacers.

Using a paper towel, wipe off as much loose dust and debris from the displacers.

Note

Inspect the top of the displacer for evicence of oil contaminations. Wet spots or paste will be present near the holes on the top of the displacer.

Bring the displacers to the appropriate processing areas.

Success

You have completed the first phase of the cold head refurbishment process.

Cold Head Sub-Assembly Processing¶

Info

At this point of the rebuild of the RDK-408A2 each of the following steps must be completed before continuing to the Assembly and Purge portion of this procedure.

Housing Teardown¶

Now that the cold head housing assembly has bee removed from the cylinder and the regenerator displacer assembly you must tear it down further. This is covered in the Gen2 Housing Assembly Teardown work instructions.

Housing Cleaning¶

Once the cold head housing assembly has been torn down it must be throroughly cleaned and inspected. This is covered in detail in the Gen2 Housing Assembly Cleaning work instruction.

Motor Refurb¶

The cold head motor assembly must also be processed in a specific way. For this model the RDK2-MTR Refurb work instructions.

Housing Assembly¶

Once the cold head motor assembly is rebuilt and the cold head housing assembly is clean it can be reassembled. For this model use Gen2 Housing Assembly Assembly work instructions.

First Stage Displacer Rebuild¶

The displacers need to be processed before they can be reassembled. For Gen2 first stage displacers use RDK2-DSP-1ST work instructions.

Second Stage Displacer Rebuild¶

For the second stage displacer, if it is a Gen2 use RDK2-DSP-2ND work instruction. Under some circumstances the Gen3 second stage displacer will be present and the RDK3-DSP-2ND work instructions must be used.

Cylinder Processing¶

The cylinder requires honing, finishing, and cleaning. For the Gen2 cylinder please use Cylinder Honing work instructions.

Assemble and Purge¶

Info

The above work instructions for the sub-assemblies must be completed to move any further.

For this phase of the refurb process you must have the following assemblies.

housing assembly
motor assembly
regenerator displacer assembly
cylinder