Receiver Adapter, Multi-Limb Vacuum

Quick Answer: A multi-limb vacuum receiver adapter, often called a cow or pig, is a glass fitting with one joint for the condenser, a vacuum side tube and several delivery limbs, each carrying its own receiving flask. Turning it on its joint moves the drip from one flask to the next, so fractions are collected under reduced pressure without admitting air.

Changing Fractions Without Breaking the Vacuum

With an ordinary vacuum adapter, every change of receiver means removing the heat, letting air into the apparatus and pumping it down again, which interrupts the boiling and can expose a hot product to oxygen. The multi-limb pattern avoids this. The adapter hangs from the condenser outlet on a greased joint, and its body carries the vacuum connection and a fan of limbs. Rotating the body a fraction of a turn lines a different limb up under the drip point, so the fore-run, the main fraction and the tail each go to a separate flask while the pressure stays steady.

The number of limbs is not stated in this listing; three and four are the common patterns, with each limb normally ending in a cone for a small round-bottomed or pear-shaped flask.

Because the whole assembly turns on one joint, that joint carries the weight of every flask and must be greased well enough to rotate smoothly under vacuum. Small receivers, each held with a joint clip, keep the load manageable.

Applications

• Fractional distillation under reduced pressure in organic synthesis and postgraduate labs
• Separating a low-boiling fore-run from the main product without letting air in
• Purifying heat-sensitive or air-sensitive liquids where re-evacuation would disturb the boiling
• Collecting samples at different head temperatures for analysis by refractive index or gas chromatography

Specifications

Care & Handling

• Grease the rotating joint with vacuum grease and turn it slowly; a dry or stiff joint can twist and snap the condenser outlet.
• Fit a clip to every receiver so no flask can drop when the adapter is turned.
• Label the receivers before the run and note the head temperature at each change.
• Release the vacuum only after the boiling flask has cooled, then remove the receivers one at a time.

Why Choose LabEquip

Research groups and advanced teaching labs that purify liquids by vacuum fractional distillation use a cow adapter to keep runs continuous. LabEquip lists it with its chemistry lab equipment and offers the complete vacuum distillation assembly; share your condenser joint size and preferred limb count on the contact page.

Frequently Asked Questions

Why is it called a cow or pig adapter?

The rounded body with several limbs hanging from it looks a little like an udder, which is where the laboratory nicknames come from. Both names refer to the same multi-limb receiver adapter.

How many fractions can I collect?

One per limb. Three- and four-limb versions are the common patterns; this listing does not give the count, so specify the number you need.

Do I need to break the vacuum to change flasks?

No. Rotating the adapter moves the drip from one limb to the next while the apparatus stays evacuated. Air is admitted only at the end of the run, after heating has stopped.

What grease should be used on the rotating joint?

A silicone or hydrocarbon vacuum grease, worked round the top third of the cone so that it spreads evenly when the body is turned. The joint should look clear with no streaks; streaks show air channels.

What size receiving flasks suit a cow adapter?

Small round-bottomed or pear-shaped flasks, since their combined weight hangs from one joint. Large receivers make rotation difficult and strain the condenser outlet.

When should I rotate to the next flask?

Watch the thermometer at the still head. Change flasks when the temperature starts to move away from its steady value, which marks the end of one fraction and the start of the next.

Last Updated: September 2026