“Low-pressure receiver” and “surge drum” both describe the same kind of vessel — a low-side liquid overfeed vessel that separates liquid from returning suction vapor and stores liquid for the recirculation pumps — and in most plants the two terms are used interchangeably. Where a distinction is drawn, “low-pressure receiver” (LPR) is the more general, code-oriented term, while “surge drum” and “recirculator” are common shop-floor names for the same vessel emphasizing its role of absorbing (surging with) swings in liquid return flow. There is no [ELI-REVIEW: ASME] or [ELI-REVIEW: IIAR-2] requirement that forces a plant to use one label over the other.
Why the naming varies by plant
Ammonia refrigeration terminology grew up regionally and by trade, and vessel names often reflect what a given engineering firm, contractor, or plant standardized on rather than a single industry-wide taxonomy. “Recirculator,” “surge drum,” “low-pressure receiver,” and “suction accumulator” overlap enough in function that the same physical vessel gets called different things on different drawings. What matters for engineering purposes is not the label but the vessel’s actual duty: does it separate liquid from suction vapor, does it feed recirculation pumps, and what liquid holdup and hold time does it need to meet.
| Common name | Usual emphasis |
|---|---|
| Low-pressure receiver (LPR) | General, code-oriented term for the low-side liquid vessel |
| Surge drum | Emphasizes buffering swings in liquid return flow |
| Recirculator | Emphasizes the vessel's role feeding overfeed pumps |
| Suction accumulator | Emphasizes compressor protection from carryover |
What actually differs, when it does
When a plant does draw a real distinction, it is usually about scope: a dedicated suction accumulator might sit only in a single suction line ahead of the compressor room, purely for carryover protection, while a low-pressure receiver or surge drum serves the whole liquid overfeed loop for one or more evaporators, with pumps drawing liquid from it. Both are sized against the same underlying checks — separation velocity, liquid holdup and hold time ([ELI-REVIEW: IIAR-2 §11.3]), MAWP, and L/D proportion — described in droplet separation velocity and suction accumulator.
Run it
ColdCalcs' Vessel Sizer covers recirculator, LPR, and surge-drum-style vessels with the same first-principles checks, and shows results on screen, free.
Open the Vessel Sizer →FAQ
Is a surge drum the same thing as a recirculator?
In most plants, yes: both terms describe the same low-side liquid overfeed vessel that separates liquid from returning suction vapor and feeds the recirculation pumps. The choice of term is usually a matter of plant or regional convention, not a functional difference.
Does it matter which name is used on a drawing?
Not for the physics, but it can matter for communication on a project. Confirming what a given label means for a specific vessel (its connections, its role in the system, and what code checks apply) is more important than the name itself.
Is a low-pressure receiver always vertical?
No. Both vertical and horizontal orientations are used; the choice affects which separation-velocity and liquid-level checks govern, and horizontal vessels are common where plant headroom is limited.
Does a low-pressure receiver need its own relief valve?
Yes, like any refrigerant-containing pressure vessel it needs pressure relief protection sized per the applicable code. ColdCalcs' calculators do not size the relief device itself; that has to be confirmed separately.