Who handles drinking water certification?
Certification for contact with drinking water belongs to the finished product and the resin grade used. Name the listed grade on the drawing, and it is run unchanged on every order.
Industry
Injection Molding for Plumbing
Plumbing parts are hidden behind walls and expected to hold pressure for decades. Nobody replaces a fitting until it leaks, and by then the water is already on the floor.
Water is hard on plastic
What years of household water do to a molded part
Each of these has ended a plastic plumbing design at some point.
Chlorine and chloramine in city water slowly attack acetal and some nylons, especially when the water is hot
Constant pressure makes plastic creep, so a part that holds on day one can weep a year later
Water hammer sends sharp pressure spikes through valves every time a tap shuts quickly
Hot water lines swing between cold and very warm many times a day
Hard water scale builds up on moving parts inside cartridges and fill valves
Resin by job
Which resins hold up where
Cold water is forgiving. Hot water with chlorine is not.
| Resin | Good for | Watch out for |
|---|---|---|
| PPSU | Hot water fittings and manifolds, strong against chlorine | Higher resin price and hot molding temperatures |
| Glass filled PPO | Pump housings, valve bodies, and meter parts in hot water | Stress cracking if assembled too tight |
| Polysulfone | Clear or translucent parts in hot water | Sensitive to some solvents and lubricants |
| Acetal | Small moving parts in cold water, low friction | Chlorine attack in hot chlorinated water |
| Polypropylene | Drain and waste fittings, toilet tank parts | Softer, so not for high pressure threads |
Threads
Metal threads in a plastic body
Plastic threads that connect to metal pipe are where plumbing parts most often split.
- Tapered pipe threads wedge outward as they tighten, and an installer with a wrench can split a plastic female thread
- A brass insert molded into the fitting takes that load, and the plastic around it only has to seal and hold the insert
- Knurls and grooves on the insert stop it from turning or pulling out under torque
- Where the insert meets the plastic is a leak path, so it gets a seal groove or an overmolded O ring seat
FAQ
Questions from plumbing product teams
Can a plastic fitting replace a brass one?
Often, yes, especially with PPSU or glass filled PPO and molded in brass threads where the fitting meets metal pipe. The pressure, temperature, and installation torque decide it.
Why did our acetal valve part crack in the field?
Hot, chlorinated water is a common cause. Acetal is excellent in cold water but degrades in hot chlorinated service. Switching to a resin made for that environment usually solves it.
Can faucet handles and escutcheons be plated?
Yes. ABS and PC/ABS take chrome plating well, which is how many handles and trim pieces get a metal look.
Keep reading
Related guides
Valves, fittings, and the resins that tolerate hot water.
Valve bodies
Pressure, sealing, and ports.
Valve bodiesPPSU
Hot water and chlorine.
PPSUPPO (Noryl)
Pump and meter housings.
PPO (Noryl)Molded in inserts
Holding metal threads in plastic.
Molded in insertsChrome plating
Metal looks on plastic trim.
Chrome platingWater treatment
Filter housings and dosing parts.
Water treatmentIndustries hub
Every sector page in one index.
Industries hubNext step
Quote the fitting with its inserts
Upload CAD with water temperature, pressure, and the resin grade your listing requires. DFM checks the thread area and insert retention first. NetProto manufacturing is ISO 9001 certified.