Oil separation in stored and injected compounds

1. What oil bleed actually is

Grease is not a solid. A thickener network holds base oil in place, like a sponge.

Oil separation, often called bleed, happens when oil leaves that network and collects as a free liquid. Bleed is a physical change. The oil has not reacted or spoiled; it has simply moved.

Some bleed is normal and even useful. A compound must release some oil to feed sliding surfaces inside a valve. The problem is not bleed itself, but bleed that is fast or one-sided, which leaves the remaining grease stiff. For the wider picture, see our valve lubrication guide.

2. Why stored drums bleed

Storage drives bleed in predictable ways. Gravity pulls free oil downward, and the oil collects where the container shape allows. Warm store rooms speed the movement, and daily temperature cycles work oil out of the matrix.

Headspace matters as well. A half-empty drum holds more air, and gives oil more room to pool. Time then does the rest. An old drum will usually show more free oil than a fresh one.

Heat is the sharpest driver of bleed. Ageing brings further changes, because oxidation alters both the oil and the thickener. Two related articles explain how valve grease ages: oxidation, bleed and hardening and how valve compounds behave at high temperature.

3. When to accept or reject a container

Judgement is visual and tactile. Work through these checks in order, and stop at the first clear failure.

1. Look at the oil layer. A thin surface film is common; a deep pool suggests the matrix has lost much of its oil.
2. Stir a sample taken from mid-drum. If the oil folds back in and the texture turns smooth, the compound is likely usable.
3. Press the grease body. Hard, cracked, or crumbly material will not recover, because the network itself has collapsed.
4. Note smell and colour. A sour smell or a clear dark shift points to oxidation rather than simple bleed.

Reject the container when the matrix has clearly failed. Stirring cannot rebuild a thickener network. We make valve lubricants in-house, and a drum that fails these checks should be rejected whoever filled it.

4. Storing drums to limit bleed

You cannot stop bleed, but you can slow it. Good storage keeps the matrix intact for longer, and costs little effort.

1. Store drums cool and out of direct sun, away from hot equipment.
2. Keep containers sealed and, where possible, indoors at a steady temperature.
3. Rotate stock, so old drums are not left at the back.
4. For half-used containers, label the date opened and use them first.

Temperature swings do more harm than a steady warm store. A cool, stable corner beats a hot wall, even when both feel acceptable. Also follow the supplier guidance printed on the drum, because compounds differ.

5. Bleed inside guns and injection equipment

Guns add pressure and standing time to the same physics. Compound left in a barrel for weeks can separate under its own weight. The first strokes may then push mostly oil.

That oil-rich shot is poor practice. It wets the fitting without carrying thickener where it matters. It also distorts your feel for the pressure response during the job.

1. Store a loaded gun for short periods only, and keep it cool and upright.
2. Purge a gun that has sat idle, and check the flow looks uniform before work.
3. Keep spare cartridges and pails sealed, rather than open beside the pump.

Simple habits prevent much of this. Routine matters more than any single repair, so see our advice on keeping sealant guns reliable.

6. What bleed means inside the valve

Bleed does not stop at the fitting. Inside the valve, some oil release is part of the design. The oil does the lubricating, while the thickener holds it in place.

Excess bleed leaves stiff pockets behind, and those pockets suggest poor distribution. A look or a feel cannot confirm it. The confirming step for a suspect valve is a seat-leak test under agreed conditions, such as pressure decay across the closed valve. Our article on field seat-leak testing methods compared sets out the options.

If you plan to inject fresh compound, the gates come first. The fittings must be in good condition, the valve design and service must suit injection, and the permit must allow the work. Inject controlled amounts within equipment and fitting ratings, and watch the pressure response. Where the valve still will not hold, the honest endpoint is a proper assessment.