Replacing lower seals on Graco pumps – Step-by-step guide

1. Complete depressurisation: an essential safety step

Before starting any maintenance operation on your Graco airless pump (Classic S, ST Max II, Ultra, Ultra XT…), it is essential to release the pressure from the system. A pump still under pressure can cause serious injury by spraying paint or suddenly releasing a mechanical part.

Here are the official steps recommended by Graco for safe depressurisation:

Steps to follow :

1. Turn the power switch to « OFF ».

2. Turn the pressure control knob fully counter-clockwise to reduce pressure to the minimum.

3. Set the discharge valve (or pressure relief valve) to the « PRIMING » position (by-pass or return).

4. To be sure of depressurisation, point the gun into an empty bucket or suitable container.

5. Press the trigger on the gun to release any remaining pressure in the spray chamber and hoses.

6. Then lock the gun trigger using the built-in safety catch.

💡 Useful tip: we recommend that you wear protective gloves and goggles and make sure that no-one is in the immediate work area.

This phase should never be neglected: it is the first barrier against accidents. Once this stage is complete, you can safely dismantle your pump.

2. Dismantling the pump – Access the set of seals to be replaced

Once the pump has been depressurised, you can move on to dismantling the lower part of the pump to gain access to the internal seals (or packings). This operation is common to several Graco models, such as the Classic S, ST MAX II, Ultra or Ultra XT.

Detailed steps :

1. Remove the suction hose
   Unscrew the suction hose and remove the strainer. This frees up access to the bottom of the pump.

2. Disconnect the pump from the frame
   Depending on the model, you may need to :

   • unscrew two or three fixing screws,

   • or release a clamp holding the pump-motor assembly to the chassis.

   📌 Tip: Tilt the pump slightly to make removal easier if it is mounted on a trolley.

3. Place the pump in a vice or on a stable workbench
   Fix the pump upside down (low-pressure side up) in a vice fitted with rubber clamps to avoid damaging the cylinder.

4. Unscrew the packing nut
   Using a flat spanner (often 1 1/4″), unscrew the top nut that holds the cartridge seals. This thread is often tightened with original threadlocker, so don’t hesitate to apply progressive pressure.

5. Pull the piston rod outwards
   Once the nut has been removed, you can carefully pull out the stem with the used seals. Sometimes a light tap with a rubber mallet is required to release the assembly if dried paint is in the way.

This step is fundamental, as it opens access to the chamber containing the seals to be replaced. This is also a good time to inspect the condition of the piston rod and its sleeve: if it is scratched or pitted, it will also need to be replaced to ensure the pump remains watertight. Otherwise, the new seals will wear out much more quickly than expected.

Pump bottom disassembly diagrams by Graco

Graco lower pump disassembly diagrams

3. Complete cleaning of piston rod and cylinder

Before installing new seals from the Graco repair kit (e.g. part no. 244194), it is essential to thoroughly clean the internal components. This will ensure a good seal and long life for the new seal system.

Why is this stage crucial?

Residues of dried paint, varnish or fine corrosion on the rod or inside the cylinder can compromise :

• correct laying of joints,

• freedom of movement of the piston,

• and ultimately lead to premature wear or new malfunctions.

Cleaning steps :

1. Wipe the whole assembly with a lint-free cloth.
   Remove large deposits and visible residues from the piston rod, thread, cylinder and inside of the pump casing.

2. Soak the parts in a suitable thinner
   If there is any dried paint, immerse the metal parts in a compatible thinner (such as white spirit or universal thinner, depending on the paint used). Leave for a few minutes.

3. Use a fine wire brush or a nylon brush
   For internal or threaded areas, a tube brush or wire brush can be used to remove persistent marks without damaging the surfaces.

4. Inspect surfaces

   • The piston rod must be as smooth as a baby’s skin, without scratches or pitting (if not, it must be replaced).

   • The cylinder must be clean, smooth and free of deposits or paint.

5. Dry thoroughly
   Before fitting new gaskets, make sure that all surfaces are completely dry and clean to avoid any contamination or slipping during assembly.

💡 Pro tip: use a compressed air nozzle to flush out residues in the deeper parts of the cylinder.

4. Installing the new seals in the kit

Once all the parts have been thoroughly cleaned and inspected, you can install the new seals contained in your Graco repair kit (for example: 244194), specific to your models: Classic S, ST MAX II, Ultra, Ultra XT, etc.

For Graco’s mid-range and top-of-the-range professional models, find all the kits and quikpaks here:

Kits & QuikPaks Graco on Airless Discounter

This kit generally includes :

• Leather or PTFE (Teflon) gaskets for dynamic sealing
• Retaining rings
• Support washers
• O-rings
• Special lubricant (depending on model)

Installation steps :

1. Identify the assembly order
   Refer to the instructions supplied with the kit (or to the official Graco documentation) for the exact order of the components. It is crucial to respect the positioning and orientation of the seals (some are conical or asymmetrical).

2. Lubricate the seals
   Apply a thin layer of the special lubricant supplied or compatible grease (from DIY shops) to the seals and stem. This will make assembly easier and extend the life of the parts.

3. Install the gaskets in the correct order in the tightening nut
   The seals are usually fitted inside the packing nut. Insert each part one at a time, pressing gently to fit them tightly. You can use a small socket, a blunt screwdriver handle or a centring pin.

4. Refit the piston rod
   Insert the rod into the cylinder, guiding it gently through the new seals. If you feel any abnormal resistance, do not insist: dismantle and check that the seals are not pinched or incorrectly positioned.

5. Screw the packing nut back on
   Once the seals are in place and the spindle installed, use a spanner to screw the nut back onto the pump body. Tighten moderately (often to 50-60 Nm depending on model). Never use a threadlocker at this stage unless specified in the manual.

💡 Tip: It’s useful to note the date of replacement and the litres sprayed on the meter if available. This helps to anticipate future maintenance.

5. Complete reassembly and repositioning of the pump

Once the new lower seals have been installed, it’s time to reassemble the Graco airless pump and replace it correctly on its bracket or frame. This step must be carried out with care to ensure that the pump is watertight, safe and in good working order when it is put back into service.

Reassembly steps :

1. Reassemble the pump casing
   Replace the internal components such as the piston, top seal and suction tube. Make sure everything is aligned correctly and that none of the seals are pinched.

2. Screw on the mechanical parts
   Screw the lower body or pump block back onto the base of the motor or chassis. Tighten with a torque spanner if possible, to Graco specifications (shown in manuals such as model 334599).

3. Reconnect the hoses
   Reconnect the suction and discharge hoses. If the return hose has a non-return valve, check that it is clean and in place. Take this opportunity to check the condition of the suction filter (replace it if it is blocked or damaged).

4. Put the pump back on its feet (Hi-Boy or Lo-Boy)
   If you have removed the pump from the trolley, screw the anchor points back onto the chassis. Make sure the pump is aligned vertically, without stressing the hoses.

5. Visually check the whole
   Before starting the engine, make sure that all components are tight, straight and clean. No tools should be left on the machine, and no hoses should be pinched or bent.

💡 Tip: If the pump’s top seal has also been replaced, make sure that the high-pressure outlet threaded sleeve is well lubricated and tightened. This will prevent any micro-leaks as soon as it is pressurised.

6. Oiling and bleeding the pump before restarting

Before restarting your freshly reassembled Graco airless machine, there’s one crucial step you need to take: oiling and bleeding the pump. This will lubricate the new seals, evacuate any air trapped in the system, and prevent any dry starts that could damage internal components.

Why is this step important?

• Freshly fitted seals must be well soaked in oil to ensure they slide smoothly and seal properly.

• Air trapped in the pump or hose can cause jerking or loss of outlet pressure.

• It allows the machine to be tested before being used with a real product.

Steps to follow :

1. Fill the lubrication reservoir (if present)
   If your model has a reservoir for maintenance oil (such as the Graco TSL), fill it according to the manufacturer’s recommendations. This will lubricate the upper piston rod.

2. Pour a little TSL oil into the pump
   Disconnect the HP outlet and pour a few drops of oil directly into the top port of the pump or through the suction pipe. This will protect the seals at first movement. (Re-apply TSL or Farbmax before each new use).

3. Set the pump to « prime » mode

   • Turn the pressure knob to minimum.

   • Open the bypass valve.

   • Switch on the machine. The paint will not come out of the gun yet, it will be redirected to the return hose.

4. Leave to run for a few seconds
   Let the pump run for 15 to 30 seconds at low pressure. Check that there are no visible leaks around the new seals or fittings. Then reset the pressure regulator to zero.

5. Close the discharge valve and start spraying
   Once the air has been expelled, close the return valve, open the airless gun and slowly increase the pressure regulator again (in an empty bucket or with water/cleaner), and check the gradual rise in pressure.

6. Final inspection
   Listen to the sound of the pump (it should be regular), test the pressure and make sure there are no leaks. Finally, leave your pump in the spray position with the gun closed at around 160 bar for 30 minutes and see whether there is any noticeable loss or whether the pressure displayed remains relatively stable. A minor loss will be tolerated.

💡 Bonus tip: Always use a specific Graco lubricant such as TSL (ref. 206994), Wagner (ref. 0508619) or Farbmax (ref. 9000069) and not conventional engine oil, to avoid premature wear of PTFE or leather seals, and mix with your own paint in the spray.

Graco offers different quantities of TSL:

 

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Questions or queries?

For any further questions or if you would like to get your hands on one of these products seen in this article, you can contact us on +49 (0) 30 220 15436, fill out our contact form or email us. If you wish to purchase one of the products mentioned above, you can check them out in our online store. You can also visit us at our service base during office hours.