---
title: "Cooling water manifold of an injection molding machine"
url: "https://www.imspares.com/injection-molding-machine-parts/hydraulics/cooling-water-manifold/"
---

# Cooling water manifold of an injection molding machine

What the cooling water manifold of an injection molding machine feeds (oil cooler, feed throat, mold circuits), its valves and flow meters, and common faults.

An injection molding machine water manifold is the pair of headers, one for supply and one for return, that distributes cooling water from the factory supply to the circuits of the machine: the hydraulic [oil cooler](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-cooler/), the cooling of the barrel feed throat and, on many machines, the mold cooling circuits through a row of valves and flow meters. It lets you switch, adjust and check every circuit in one place. When a circuit is blocked or starved of water, the effect shows up elsewhere: hot hydraulic oil, pellets sticking in the feed throat, or longer cycles and warped parts.

## What the water manifold feeds

- **The oil cooler.** This circuit keeps the hydraulic oil at its working temperature. It often has its own control valve, worked by hand, by a thermostat or by a solenoid switched by the controller. The cooler appears in the hydraulic system drawing on the return line. See [oil temperature](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-temperature/).
- **The feed throat.** Water flows through the feed throat under the hopper, so the pellets stay solid until the screw takes them in. See the [hopper and feed throat](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/hopper-and-feed-throat/).
- **The mold circuits.** Hoses with quick couplings connect each mold cooling channel to an outlet on the supply header and an inlet on the return header. Molds that need a controlled temperature are often connected to a separate mold temperature controller or chiller instead.

## How the water manifold is built

- A **supply header** and a **return header**, each with a row of outlets.
- A **valve** on each circuit, usually a ball valve to switch it or a needle or regulating valve to set the flow.
- **Flow meters** or flow indicators, often a float in a transparent tube, so you can see the flow in each circuit. Some machines have temperature gauges or electronic flow and temperature monitoring.
- **Main inlet and outlet valves**, often with a **strainer** at the inlet to catch scale and debris.
- **Quick couplings** and hoses to the mold.

The water usually comes from a cooling tower or a chiller. The supply temperature, pressure and water quality the machine needs are given in its manual. The flow through every circuit depends on the pressure difference between the supply and the return, so a restricted return line lowers the flow everywhere.

## Common water manifold problems

- **Low flow in one circuit**: scale or dirt in the mold channels, a kinked or collapsed hose, a partly closed valve, a damaged quick coupling or a flow meter float stuck in its tube.
- **Low flow in every circuit**: a blocked inlet strainer, a main valve not fully open, low supply pressure or a restricted return.
- **Leaks** at quick couplings, O-rings, threaded joints and flow meter seals.
- **Dirty or cracked flow meter tubes** that can no longer be read.
- **Scale and corrosion** inside the headers and valves from untreated water.
- **Condensation**: when the water is colder than the dew point of the air, the manifold, hoses and mold sweat. The water drips onto the machine and can cause rust and water marks on the parts.

## What a water problem looks like on the machine

- **Oil cooler circuit**: the hydraulic oil runs hotter than usual. The oil cooler page explains how to tell a water problem from a fouled cooler.
- **Feed throat circuit**: pellets soften and bridge in the throat, and the screw takes longer to recover or starves.
- **Mold circuits**: uneven mold temperatures, longer cooling times, warpage and [sink marks](https://www.imspares.com/blog/sink-marks-injection-molding-causes-solutions/).

## Maintenance

1. Clean the inlet strainer regularly, and more often if the water is dirty.
2. When the mold and machine are running well, note the normal flow on each flow meter. A change from that value is the first sign of a blockage.
3. Flush and descale the mold circuits when flows drop, and blow the water out of the mold with air before storing it.
4. Replace worn quick couplings, hoses and O-rings before they leak.
5. Keep the oil cooler circuit open and working whenever the pump runs.
6. Drain the manifold and the oil cooler if the machine will stand in a building that may freeze.
7. Use treated water. Hard or untreated water scales the cooler, the feed throat and the mold channels.

## What to send for a replacement quote

1. The machine brand and model.
2. The number of circuits on the manifold.
3. The inlet and outlet thread sizes, and the thread size and spacing of the circuit outlets.
4. The type and flow range of the flow meters, if fitted.
5. The material and the mounting arrangement.
6. Photos of the whole manifold and of any part you want replaced, such as a valve, flow meter or coupling.

[Request a quote](https://www.imspares.com/request-quote/). For the hydraulic side of the machine that the cooling water protects, see the [hydraulic system guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/).

## Questions

### What does the water manifold on an injection molding machine do?

It distributes cooling water from the factory supply to the machine's circuits, usually the hydraulic oil cooler, the feed throat and the mold cooling circuits, and collects the water coming back. Its valves and flow meters let you set and check each circuit in one place.

### Why is the water flow low on one mold circuit?

Usually because of a blockage in that circuit: scale or dirt in the mold channels, a kinked or collapsed hose, a partly closed valve, a faulty quick coupling or a stuck flow meter float. If every circuit is low, look at the inlet strainer, the main valves and the supply pressure instead.

### What water temperature and pressure should the machine be supplied with?

The machine manual specifies the supply temperature, pressure and water quality for the oil cooler and the other circuits. Mold circuits are set to suit the mold and the material, often through a separate mold temperature controller or chiller.

### Why does the water manifold drip even though nothing is leaking?

That is condensation. When the water is colder than the dew point of the surrounding air, moisture condenses on the manifold, hoses and mold. Insulate cold lines or raise the water temperature where the process allows it.