Pump pair — Inzonex Modular Insulation, hot-water skid
Pumps / Types
Circulation pump types
On a hot-water circuit the choice is made three times over.
Three separate decisions describe a pump: how the shaft is sealed, how the pump is held up, and how its speed is controlled. A pump carries all three at once. A glandless inline twin-head on variable speed and a glanded base-mounted single at fixed speed both circulate hot water. Almost nothing else about owning them is the same.
The seal
Glandless against glanded
Glandless, or wet rotor
The rotor runs in the pumped water and the motor is sealed to the casing. There is no shaft seal to leak and nothing to replace. The water also cools and lubricates it. It is quiet, and it will not tolerate running dry. It covers most building-services duty.
Glanded, or dry rotor
The motor is separate and the shaft passes through a mechanical seal. It takes higher duties and higher temperatures than a wet rotor will. In exchange, the seal is a wear part with a life and a leak path.
Which one is on the skid
The pumps in this frame are inline units with the motor sitting directly on the volute. The casing runs at line temperature whichever type it is, and that is the surface this tool is counting.
The mounting
Inline, end-suction, twin
Inline
Suction and discharge are on the same axis, so the pump drops into the pipe run and is carried by it. It takes no floor and it is the normal choice in a plant room where space is the constraint.
End-suction and base-mounted
The pump sits on a plinth with suction on the end and discharge on top. It takes more room and more pipework, and it is easier to work on because motor and pump come apart independently.
Twin head
Two pumps in one casing with a changeover flap, one running and one on standby, alternating automatically. It gives duty and standby in the space of one pump, and it means one of the two impellers is stationary at any moment.
The control
Fixed and variable speed
Fixed speed
The pump runs at one speed and the system is balanced around it. Simple, and it moves the same water whether or not anything is calling for heat.
Variable speed
The pump varies its speed against a control curve - constant pressure, or proportional pressure that lets the head fall as flow falls. On a circuit with two-port control valves it is the difference between a pump that throttles itself and one that fights the valves.
What it does not change
The casing is still at line temperature whenever the circuit is hot, whatever the speed. Pump control saves electrical energy; it does nothing about the heat leaving the casing into the room.
Reference
Type against duty
| Type | How it is arranged | Shaft seal | Where it belongs |
|---|---|---|---|
| Glandless inline | Rotor in the pumped water | None to replace | Most building services and DHW |
| Glanded inline | Mechanical seal on the shaft | Seal is a wear part | Higher duty and temperature |
| End-suction base-mounted | On a plinth, own baseplate | Mechanical seal | Large duties, easier overhaul |
| Twin head | Two impellers, one casing | As the type it is built on | Duty and standby in one footprint |
Type · How it is arranged · Shaft seal · Where it belongs
Asked about circulation pump types
Questions.
Answers distinguish modelled heat-loss estimates from equipment selection and service guidance.
What is a glandless circulation pump?
One where the rotor runs in the pumped water and the motor is sealed to the casing, so there is no shaft seal at all. The water cools and lubricates the bearings, which makes it quiet and maintenance-free, and also means it must never be run dry. It is the standard pump on building-services hot water.
What is the difference between an inline and an end-suction pump?
An inline pump has suction and discharge on the same axis and is carried by the pipework, so it takes no floor space. An end-suction pump sits on a plinth with its own baseplate and needs more pipework. It is easier to overhaul, because the motor and the pump come apart separately.
What is a twin head pump for?
Duty and standby in one casing. Two impellers share a body with a changeover flap, and one runs while the other waits. The controller alternates them so neither sits still long enough to seize. It gives redundancy without a second set of pipework.
Does a variable speed pump reduce heat loss?
No. It reduces the electrical energy the pump draws by matching speed to demand. The casing still sits at line temperature whenever the circuit is hot. How fast the impeller turns does not change the heat leaving that casing into the plant room.
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More on pumps
The node page carries the heat-loss figures and the size table.