What you gain
- No corrosion or scale buildup inside the flow path
- Mounting feet, ports, and motor flange molded into one part
- A smooth molded flow path with little or no machining
Molded part guide: pump housings
Injection Molded Pump Housings
A pump housing sits full of fluid under pressure, often warm, sometimes hot. Plastic handles that well when the resin and the wall layout are chosen for it, and badly when a metal design is simply copied.
The job
The load never goes away
Most housings see load now and then. A pump housing sees it constantly, and that changes how the plastic behaves.
Plastic under steady load slowly moves. It is called creep, and it gets worse with temperature. A housing that measures fine on day one can open up at a flange, loosen a threaded port, or relax an O-ring squeeze after months of warm, pressurized service. Resin choice and stiffening are driven by that long-term behavior, not by a short-term strength number.
The fluid matters as much as the pressure. Hot water and glycol coolant attack some resins through hydrolysis, and cleaning chemicals attack others. Always tell us what flows through the pump, at what temperature, and for how long.
Pressure cycling adds fatigue. Every start, stop, and water hammer event flexes the housing a little, and cracks tend to start where the plastic is already weakest: weld lines, sharp internal corners, and the root of a threaded port.
Fluid and resin
Starting points by service condition
Common choices, not a recommendation for your pump. Final resin comes from your fluid, temperature, and approvals.
| Service | Resins often used | Why |
|---|---|---|
| Cool water, garden and sump pumps | Polypropylene, glass-filled polypropylene | Good chemical resistance, and glass adds stiffness |
| Hot water and engine coolant | Glass-filled PPS, hydrolysis-stabilized glass-filled nylon | Hold shape and strength in hot water and glycol over long exposure |
| Hot water with frequent sterilizing or high pressure | PPSU, polysulfone | Tough, hydrolysis resistant, and some grades are transparent |
| Chemical dosing and aggressive fluids | Polypropylene, PPS, or a fluoropolymer chosen by chemistry | Chemical resistance leads, strength is solved with geometry |
| Drinking water | A grade listed for potable water in your market | The listing is held by the resin grade or the finished product, so the grade is fixed early |
Service tiers
Pump housing service tiers and quote path
Housing tier for this family: Wet, pressurized service: resin, creep, and port weld lines. Upload CAD with seal path, fasteners, and heat sources called out in notes when they are not modeled.
| Tier | Environment | What matters most | Typical molded route | Quote path |
|---|---|---|---|---|
| 1 Cool water | Garden and sump pumps | The pressure stays on | PP, or glass-filled PP for stiffness | Upload CAD; name the fluid |
| 2 Hot water or coolant | Hot water and glycol | Hydrolysis, and creep gets worse when warm | Glass-filled PPS, or hydrolysis-stabilized nylon | Instant quote; name the fluid |
| 3 Sterilizing service | Hot water, sterilized often | The resin has to stay tough in that water | PPSU or polysulfone, when the drawing names it | Upload CAD; name the service |
| 4 Chemical dosing | Aggressive fluids | The chemistry picks the resin | PP, PPS, or the fluoropolymer the fluid names | Instant quote; name the fluid |
| 5 Ports | Inlet and outlet | A weld line on the far side of each port | Gate so it stays off the port root and the seal face | Upload CAD; note the ports |
Materials
Resin families: quick reference for quote notes
One primary family per shell line item. Put the fluid and the service temperature in comments.
| Family | Typical use on this part type | Notes for instant quote |
|---|---|---|
| PP | Cool water, and many chemicals | Field PP; name the fluid |
| Glass-filled PPS | Hot water and coolant | Field PPS |
| Glass-filled nylon | Hot water when the grade is hydrolysis-stabilized | Field nylon; name the fluid |
| PPSU | Hot water with sterilizing, when the drawing names it | Field PPSU |
Volute and ports
The shape of the flow path sets how the tool is built
Two features drive most of the tooling decisions on a pump housing.
A centrifugal volute spirals and widens around the impeller, which is an undercut in almost every direction. Most molded pumps split the volute on its mid plane, or at the face of the impeller, into a body and a cover that are sealed together. That keeps the tool to straight pulls with a few side actions for the ports, rather than a collapsing core.
Every inlet and outlet port is a hole the plastic has to flow around, so each one tends to create a weld line on its far side. That is the wrong place for a weak spot on a pressurized part. Gate location is chosen so weld lines fall away from port roots and sealing faces, and DFM review shows where they are expected to land.
Threaded ports can be molded directly or carry a metal insert. Metal inserts stop thread creep and let a fitting be tightened repeatedly, at the cost of a loading step in every cycle.
Replacing metal
Moving a pump body from cast metal to molded plastic
Conversion works well on many pumps, but not by copying the metal part.
What you have to design for
- Creep and fatigue at temperature, which metal barely shows
- Stiffness comes from ribbing and shape, since thick plastic walls sink and void
- Pressure and life testing on molded samples, in the real fluid
Avoid these
Common design mistakes on pump housings
Two choices that leave a weak port, or copy a thick metal wall.
A weld line left at a port root or on a sealing face. That is where a pressurized housing is already weak. Place the gate so the weld line lands away from both.
Copying a thick metal wall into plastic. Thick sections sink and void. Use a thinner, even wall, and add ribs where the load goes.
Drawing
What to send with a pump housing
Operating conditions matter as much as the CAD here.
The fluid, its temperature range, and any cleaning chemicals
Working pressure, peak pressure, and how often the pump cycles
Port connections and whether they carry metal inserts
How the body and cover seal: O-ring, gasket, or welded
Any potable water or food contact listing the product needs
The impeller and motor mounting, so the fit up can be checked
Keep reading
Related guides
Materials and rules for wet, pressurized parts.
PPS
Hot water and coolant service with low creep.
PPSPPSU
Tough and hydrolysis resistant for hot water.
PPSUPolypropylene
Chemical resistance for cool water and many fluids.
PolypropyleneMetal to plastic conversion
Redesigning a cast part instead of copying it.
Metal to plastic conversionWeld line strength
Keeping knit lines off pressurized features.
Weld line strengthMolded threads vs inserts
Choosing how ports take a fitting.
Molded threads vs insertsUndercuts
Side actions for ports and flow paths.
UndercutsFilter housings
Threaded bowls that also run under pressure.
Filter housingsMolded parts library
Every part-type guide, grouped by family.
Molded parts libraryImpellers
The rotating part inside the pump volute.
ImpellersWater treatment
Dosing pump heads and housings.
Water treatmentFAQ
Questions about molded pump housings
Can you mold the impeller as well as the housing?
Yes. Impellers are often molded in the same resin family as the housing. Balance and blade thickness get reviewed in DFM, since a thick hub next to thin blades is a common source of sink and distortion.
Do you pressure test the housings?
Inspection follows the plan agreed for your part. Pressure, burst, and life testing of the pump are normally run by your team on molded samples, in the real fluid and temperature.
Can you provide a potable water certified housing?
We mold with the listed grade you specify. The listing itself belongs to the resin supplier or to your finished product, not to NetProto.
Our metal pump body is thick everywhere. Can it be molded as is?
Usually not well. Thick plastic sections sink, void, and take a long time to cool. The usual route is a thinner, even wall with stiffening where the load goes, which DFM feedback helps lay out.
Why name the fluid before the resin?
Hot water and glycol attack some resins. Cleaning chemicals attack others. The resin is chosen for that service, not from a short-term strength number.
Why split the volute?
A spiral volute is an undercut in almost every direction. Splitting it on the mid plane, or at the impeller face, keeps the tool to straight pulls plus side actions for the ports.
Next step
Quote the body, cover, and impeller
Upload the housing CAD and tell us the fluid and temperature. DFM feedback flags weld lines at ports, thick sections, and how the volute splits.