Molded body
- Passages, seats, and mounts come out together
- Every body is the same once the process is set
- Needs a tool, with actions for cross passages
Molded part guide: valve bodies
Injection Molded Valve Bodies
A valve body looks like a solid block with holes through it. Molded in plastic it cannot be solid, and the holes cannot all point the same way. What makes a good molded valve body is how much material is taken out of the thick areas, and how the passages that cross the pull direction are formed.
Thick and hollow
Solid blocks do not mold well
Ball valve bodies, check valve bodies, diverter bodies, and solenoid valve housings.
A machined valve body starts as a solid block and has passages drilled into it. A molded body cannot copy that. A thick section of plastic cools from the outside in, and the middle is still liquid long after the skin has frozen. As the middle shrinks it pulls material inward, leaving either a sunken outer surface or a hollow void right where the body needs its strength.
The answer is to take the material out on purpose. The body becomes a shell of fairly even section, with hollow pockets where the solid block used to be, and thin stiffening webs where load has to travel. Anything that must stay solid, such as a seal seat or a threaded port, is kept as small and local as possible so it cools at a similar rate to the shell.
Then there are the passages. A passage that runs along the direction the tool opens can be formed by a simple core. A passage that crosses that direction needs a side action: a slide or a lifter that pulls sideways before the body is pushed out. Each one adds cost and a parting line on the surface it forms, so the design usually tries to align as many passages as possible with the pull direction.
Seals are the last piece. Where an O-ring or a seat presses against the body, the surface has to be round, smooth, and not distorted by shrinkage from a nearby thick spot. Threaded ports are either molded with an unscrewing core, or made from a metal insert molded into the body where the joint will be tightened repeatedly.
Features
Valve body features and how they are made
Every feature has a tooling consequence.
| Feature | Purpose | Design note |
|---|---|---|
| Through passage | Main flow path | Formed by a core along the pull direction |
| Cross passage | Side port or bypass | Needs a slide or a lifter |
| Seal seat | Where the O-ring or seat presses | Round, smooth, and free from nearby thick spots |
| Threaded port | Connects to the line | Unscrewing core, or a molded-in metal insert |
| Hollow pockets | Replace solid material | Even shell section with thin stiffening webs |
Thick sections
Solid areas pull themselves hollow
What looks like strength in a machined body becomes a void in a molded one.
- A thick area freezes on the outside while the middle is still liquid
- As the middle shrinks it pulls inward and leaves a sunken face or a hollow pocket
- Hollowing the body out on purpose gives an even section that cools together
- Anything that must stay solid is kept small and local
Making the body
Molded valve body or machined valve body
Machining suits low counts and one-off sizes. Molding suits repeat production.
Machined body
- No tool, so changes are quick
- Any passage direction is possible
- Each body costs the same to make as the last
Drawing
What to send with a valve body
The passages and the seals set the tooling plan.
Body CAD with all passages shown
Seal type and where each one presses
Port connections and thread callouts
Fluid, temperature, and working conditions
Any surface that has to stay smooth
Expected annual volume
Keep reading
Related guides
Other fluid parts, coring, and the voids that hide in thick sections.
Manifolds
Several passages in one body.
ManifoldsPump housings
Casings around a rotor.
Pump housingsNozzles
Orifices and spray patterns.
NozzlesIrrigation fittings
Barbs, threads, and sunlight.
Irrigation fittingsVoids
Hollow pockets in thick areas.
VoidsUndercuts
Features that block the pull direction.
UndercutsMolded threads vs inserts
Plastic thread or metal insert.
Molded threads vs insertsIndustrial and transportation
How we support industrial programs.
Industrial and transportationMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded valve bodies
Can a machined valve body be copied as a molded one?
Rarely feature for feature. The solid areas have to be hollowed out and the passages rearranged around the pull direction. The function stays the same, but the shape usually changes a lot. Rebuilding the body as a shell with hollow pockets usually keeps every function while removing the thick areas.
Why are there sunken marks on the outside of the body?
A thick area behind that surface shrank and pulled it in. Coring out the area behind it, or splitting a heavy junction into thinner webs, removes the mark. Checking the first molded bodies against the drawing at the seal seats, rather than only at the ports, catches this early.
How many side actions are too many?
There is no fixed limit, but each one adds tool cost, cycle time, and a parting line. Turning a passage so it runs along the pull direction is usually worth a small design change.
Should the threaded ports be molded or inserted?
Molded threads suit ports that are assembled once. A molded-in metal insert suits a port that is opened and closed repeatedly, or torqued hard.
Next step
Quote a valve body with its passages
Upload the body and mark the passages and seal seats. DFM feedback covers coring, side actions, seat roundness, and thread choice.