When to Change your HPLC Piston Seal

Example of polymer side vs. energizer side of seal.

Note stainless steel energizer shown. Seal could have fluoropolymer O-ring energizer instead (black O-ring).

It is recommended to change your HPLC pump’s piston seals during planned preventative maintenance. With regular pump usage, this is recommended every six months. And, remember, if you have a dual-piston pump, you have two piston seals to replace.

Symptoms That Indicate a Piston Seal Change Is Due

Lower-than-normal pressure, pressure variations, and leaks in the pumping system can all indicate possible problems with the piston seal. Depending on the fluid or mobile phase used, piston seal replacement is often necessary after 1000 hours of running time.

How To Replace a Piston Seal on a Chrom Tech HPLC Pump

Removing the Seals

1. Remove the pump head and self-flush assemblies as described above.
2. Remove the backup washer if it is present in the pump head.
3. Insert the flanged end of the seal insertion/removal tool into the seal cavity on the pump head. Tilt it slightly so that flange is under the seal and pull out the seal.
4. Repeat the procedure for the low-pressure seal in the flush housing.

Replacing the Seals

1. Place a high-pressure replacement seal on the rod-shaped end of the seal insertion/removal tool so that the energizer is visible when the seal is fully seated on the tool. Insert the seal into the pump head. Be careful to line up the seal with the cavity while inserting. Then, withdraw the tool, leaving the seal in the pump head. When looking into the pump head cavity, only the polymer side of the seal should be visible.
2. Place a self-flush replacement seal on the seal insertion/removal tool so that the energizer in the seal is visible when the seal is on the tool. As in the previous step, insert the tool and seal into the seal cavity on the flushing housing, taking care to line up the seal with the cavity, and then withdraw the tool. When the seal is fully inserted, only the polymer side of the seal will be visible in the seal cavity. NOTE: If the self-flush feature is not being used, install the provided guide bushing in the place of the self-flush seal.
3. Place the seal back-up washer over the high-pressure seal in the pump head.
4. Replace the self-flush and pump head assemblies.
5. Condition the new seals as described below.

Conditioning New Seals

New seals should be conditioned prior to use. Conditioning is the process of running the seals wet under controlled conditions to allow surfaces to seat and to prepare the seal for operation. Use only organic solvents to condition new seals. Buffer solutions and salt solutions should never be used to condition new seals. Recommended solvents are HPLC-grade methanol and isopropanol, as well as water mixtures of either. Suggested Conditioning Parameters: using a restrictor coil or a suitable column, run the pump with a 50:50 solution of isopropanol (or methanol) and water for 30 minutes at the back pressure and flow rate listed under PHASE 1 in the following chart and according to the pump head type. Then, run the pump for another 15 minutes under conditions for PHASE 2 in the following chart, according to pump flow and pressure capabilities.

I Changed My HPLC Piston Seals; What About the Piston?

Any time piston seals are replaced, the piston rod should be inspected with a 10x magnifier or microscope to ensure it does not have wear or scratches. Replace the rod if you observe any glazed regions or scratches.

How To Clean the Piston and Replacing the Piston in Chrom Tech Pumps

Cleaning the Piston

1. After the pump head and self-flush housing are removed, gently remove the backup seal plate from the pump housing, using either a small screwdriver or toothpick in the slot on top of the pump housing.

2. Grasp the metal base of the piston assembly to avoid exerting any side load on the sapphire rod, and remove the piston from the slot in the carrier by sliding it up.

3. Use the scouring pad included in the seal replacement kit to clean the piston. Gently squeeze the piston within a folded section of the pad and rub the pad along the length of the piston. Rotate the pad frequently to assure the entire surface is scrubbed. Do not exert pressure perpendicular to the length of the piston, as this may cause the piston to break. After scouring, use a lint-free cloth, dampened with alcohol, to wipe the piston clean.

4. To reinstall the piston, grasp the metal base of the piston assembly and insert it into the slot in the piston carrier until it bottoms in the slot.

Replacing the Piston

Remove the pump head and self-flush assemblies.

1. Grasp the metal base of the piston assembly to avoid exerting any side load on the sapphire rod, and remove the piston from the slot in the carrier by sliding it up.

2. Grasp the metal base of the replacement piston assembly and insert it into the slot in the piston carrier until it bottoms in the slot.

3. Replace the pump head.

Improving Seal Life: Recommended Use of Self-Flush Feature

Self-Flushing Pump Head

Self-flushing pump heads provide continuous washing of the piston surface without the inconvenience of a manual flush or gravity feed arrangement. The self-flushing two-pump head uses a self-flush seal and secondary set of check valves to create a continuous and positive flow in the area behind the high-pressure pump seal. The flushing solution washes away any buffer salts that have precipitated onto the piston. If not removed, these precipitates can abrade the high-pressure seal and cause premature seal failure and leakage, and can possibly damage the pump.

Recommended Use of Self-Flush Feature

It is strongly recommended that the Self-Flush feature be used to improve seal life in a number of applications. In particular, (as stated above) if pumping Buffers, Acids/Bases, or any inorganic solution near saturation, the pump must utilize the Self-Flush feature. With every piston stroke, an extremely thin film of solution is pulled back past the seal. If this zone is dry (without use of Self Flush) then crystals will form during continuous operation, which will ultimately damage the seal. Another application where Self Flush is highly recommended is when pumping Tetrahydrofuran (a.k.a. THF, Diethylene Oxide) or other volatile solvents such as acetone (Note: THF and most solvents are compatible only with all-Stainless-Steel systems. THF will attack PEEK). Volatile solvents will dry rapidly behind the seal (without the use of Self-Flush), which will dry and degrade the seal. Solutions of either 100% IPA, 100% Methanol, 20% IPA/water mix, or 20% Methanol/water mix are the required choices for the flush solution. Do not use only water for the self-flush solution (e.g., DI water, tap water, filtered water), as water alone can cause abrasion of the high-pressure piston seal, as well as the self-flush seal.

Preparation for HPLC Pump Storage

Isopropanol Flush Disconnect the outlet tubing from the pump. Place the inlet filter in isopropanol. Use a syringe to draw a minimum of 50 ml through the pump. Pump a minimum of 5 ml of isopropanol to exit. Leave the inlet tubing connected to the pump. Place the inlet filter in a small plastic bag and attach it to the tubing with a rubber band. Plug the outlet port with the shipping plug, leave a length of outlet tubing on the pump, or cover the outlet port with plastic film.

CONCLUSION

Routine care and maintenance of your HPLC pump will minimize unplanned downtime in the laboratory. When replacing piston seals, it is important to inspect the piston rod. Scratches or precipitates on the piston rod can abrade the high-pressure seal and cause premature seal failure and leakage.

Chrom Tech offers HPLC Accessories, including Agilent HPLC Instrument Replacement Parts and Instrument Replacement Parts for other vendors HPLC pumps. If you have an old Alltech pump, contact Chrom Tech, as we carry many of the Alltech Pump replacement parts in stock.