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Semi-Open Impeller

Back shroud only. The vanes run open against the casing face.

Semi-Open Impeller

Back shroud only. The vanes run open against the casing face.

Losing the front shroud costs a little efficiency and buys two things: the passages are easier for solids to get through, and the running clearance can be re-set in service by moving the impeller along the shaft instead of replacing wear rings.

For most aftermarket water and light-slurry duty that trade is worth making. The vane profile still has to be reproduced properly — an open vane is no more forgiving hydraulically than a closed one.

Casting process	Vertical-line sand moulding on two lines (national patent)
Materials	Grey iron · ductile iron · WCB carbon steel · CF8M stainless
Machined features	Bore and keyway · back shroud face · vane tip diameter and face · balance correction
Minimum order	100 pieces
Certification	EN 10204 3.1 per heat, spectrometer results
Source of geometry	Your drawing, 3D file or a worn sample

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Casting Notes

What Is Difficult About This One

Every casting has one or two features that decide whether the batch repeats. On this part they are these.

Open vanes draw straight off the pattern

No enclosed passage means no trapped core. It is the simplest of the impeller constructions to cast soundly.

Vane tips are the thin edge

They are the last to fill and the first to erode. Gating is arranged so the tips are not at the end of the longest run.

Vane roots need feeding

Where the vane meets the shroud is the thick junction. Shrinkage there is the classic defect on this construction.

Materials

Alloy Options

The same geometry is a different part in three different plants. Chloride content, abrasion and temperature drive the choice — not the name of the fluid.

Alloy	Grade	When it is the right choice
Grey iron	HT200 / HT250	Default for water duty. Damps vibration, machines easily, lowest cost.
Ductile iron	QT450 / QT500	When the duty is cyclic or the part takes shock. Tougher than grey.
WCB carbon steel	ASTM A216 WCB	Higher strength, weldable. For pressure-bearing bodies.
CF8M stainless	ASTM A743 CF8M	Chloride and corrosion duty — the cast equivalent of 316.

Enquiry

What to Send Us

These are the ones specific to this part. A drawing, a 3D file or the worn original covers all of them at once.

Item	Why it matters
Shaft diameter and key size	The fit that has to be right
Vane count and outlet angle	Or send the worn impeller — we measure it
Direction of rotation	Seen from the drive end; the question most often forgotten