Proportional Valves and Amplifier Cards in Injection Moulding: Getting Repeatable Shot Control
If a moulding machine is producing shorts on some shots and flash on others while every setting on the controller is unchanged, the problem is usually not the mould and not the material. It is the hydraulic control loop, and specifically the proportional valve and the amplifier card driving it.
Yashvi Hydraulics supplies both, and we see the same pattern constantly: a plant replaces a valve, the machine improves for a fortnight, and the fault returns because the card was never looked at. This article explains how the pair works together and what to check.
Why on-off valves cannot hold a moulding tolerance
A conventional solenoid directional valve has two states. The spool is either shifted or it is not. Flow is either full or nothing, and speed is set by a separate flow control valve that was adjusted once and forgotten.
Injection moulding does not work that way. A good shot needs a fast fill through the thin sections, a controlled deceleration before the cavity is full to avoid flash, a switchover to holding pressure at a precise point, and a controlled decompression. That is a velocity profile, not an on-off command, and a discrete valve cannot produce it.
How a proportional valve works
A proportional valve uses a proportional solenoid whose force is proportional to the current in its coil, opposed by a spring. Increase the current, the spool moves further, the metering notches open further, and flow increases. The spool can sit anywhere between closed and fully open rather than at one of two positions.
That gives you three things a discrete valve cannot: infinitely variable flow so actuator speed can be profiled through the stroke, controlled acceleration and deceleration through current ramping so the machine stops shocking itself, and remote adjustment from the machine controller instead of a screwdriver on a needle valve.
Better valves add spool position feedback through an LVDT, which closes the loop around spool position and removes the effect of flow forces and friction. If your application needs genuine repeatability, ask Yashvi Hydraulics for a closed-loop valve rather than an open-loop one.
The amplifier card is half the system
A proportional valve cannot be driven directly from a controller output. It needs a proportional amplifier card, which takes the command signal, typically 0 to 10 volts or 4 to 20 milliamps, and converts it into a precisely regulated coil current.
The card does more than convert. It regulates current in closed loop so coil heating does not change the valve response as the shift warms up, it applies dither, and it shapes the command with ramps and deadband compensation. A card that is mismatched to the valve will produce a machine that appears to have a valve fault.
The four adjustments that matter
- Gain. Sets how much coil current a given command produces, and therefore the maximum speed at full command. Too high and the axis overshoots and hunts. Too low and the machine never reaches its programmed velocity.
- Ramp. Sets how quickly the command is allowed to change. Ramps stop pressure shocks in the lines and give smooth acceleration into and out of each phase. On a moulding machine, ramp settings often make the difference between clean switchover and a pressure spike that flashes the part.
- Dither. A small oscillating current superimposed on the command that keeps the spool in constant micro-movement so it never sticks. Too little dither and the valve exhibits hysteresis and stiction. Too much and you get visible pulsing in actuator movement. Both frequency and amplitude are adjustable on most cards.
- Deadband compensation. Also called jump or offset. Proportional spools have an overlap where small commands produce no flow at all. This setting steps the current straight past the dead zone so the axis responds immediately to a small command.
These four interact. Change the gain and you will usually need to revisit the ramp. Yashvi Hydraulics supplies cards matched to the valve so the starting point is sensible rather than arbitrary.
Common faults and what they look like on the machine
| Symptom on the machine | Usual cause |
|---|---|
| Axis does not move until the command is well above zero | Deadband compensation not set |
| Movement is jerky at low speed | Dither too low, or contamination causing spool stiction |
| Visible pulsing at steady speed | Dither amplitude too high |
| Overshoot and hunting at the end of a move | Gain too high, or ramp too short |
| Machine never reaches programmed velocity | Gain too low, or supply flow insufficient |
| Response changes as the shift progresses | Card not regulating current in closed loop, or coil overheating |
| Shot-to-shot variation with no setting changes | Contamination in the valve, or a failing card output stage |
Note how many of these look identical to a mechanical fault. Before condemning a valve, put a meter on the card output and confirm the current is actually following the command.
Contamination is the silent killer
Proportional and servo valves have far tighter internal clearances than standard directional valves. A particle that a directional valve would pass without noticing will hold a proportional spool off its intended position and destroy repeatability.
Fit pressure line filtration immediately upstream of every proportional valve, target a cleaner ISO 4406 code than you would for the rest of the system, and change elements on schedule rather than on failure. Yashvi Hydraulics supplies filter elements in the fine micron ratings these valves need.
Proportional valve or proportional pump?
Both control flow, but they solve different problems. A proportional pump varies displacement at source, so the system only ever generates the flow it needs. That is the energy-efficient approach and it keeps oil temperature down, which matters on machines running continuously.
A proportional valve controls flow at the actuator, which gives faster dynamic response and lets you control several axes independently from one supply. Many moulding machines use both: a variable displacement pump setting the overall supply and proportional valves shaping the individual movements.
If you are specifying a system rather than replacing a part, talk it through with Yashvi Hydraulics before you commit. The right architecture saves more in running cost than the component price difference.
Ordering the pair correctly
When you enquire, give Yashvi Hydraulics the valve model code, the coil voltage and current rating, the command signal type your controller produces, whether the valve has spool position feedback, and the mounting pattern. Valve and card must be matched. A card sized for a different coil will either fail to drive the valve fully or run the coil beyond its rating.
We supply proportional valves, matched amplifier cards, and the full hydraulic valve range across India and for export to Dubai, Abu Dhabi and further afield.
Proportional Valve and Card Supply Across India and the UAE
Yashvi Hydraulics supplies proportional valves and matched amplifier cards to injection moulding plants, machine tool builders and OEMs across India. Plastics clusters we serve regularly include Delhi NCR and Noida, Mumbai and Pune, Ahmedabad and Rajkot, Kolkata, Chennai, Coimbatore, Bengaluru and Ludhiana.
In the Gulf, Yashvi Hydraulics ships proportional valves and cards to Dubai, Abu Dhabi, Sharjah, Jebel Ali, Dammam and Riyadh, where moulding plants running continuous shifts cannot afford a valve to sit on backorder. Because the valve and the card must be matched, Yashvi Hydraulics supplies them as a pair with recommended starting settings for gain, ramp, dither and deadband. We also export to Kenya, South Africa, Saudi Arabia, Russia and the United States.
Frequently Asked Questions
Can I use any amplifier card with any proportional valve?
No. The card must match the coil’s current rating and the valve’s characteristics. Using a generic card usually gives poor low-end response and unstable behaviour at speed. Send the valve model to Yashvi Hydraulics and we will supply the correct card.
What is the difference between a proportional valve and a servo valve?
Servo valves have finer machining, near-zero spool overlap and much higher bandwidth, and they demand very clean fluid. Proportional valves are more tolerant and less expensive, and they are sufficient for the great majority of industrial applications including most injection moulding.
My valve was replaced but the fault came back. What now?
Check the card before replacing the valve again. Measure the coil current against the command signal across the full range. If current does not track command linearly, the card is the fault. This is the single most common misdiagnosis we see.
Does Yashvi Hydraulics help with tuning?
Yes. When we supply a valve and card together we provide the recommended starting settings for gain, ramp, dither and deadband, and our team will talk your engineer through commissioning on the phone.
Get the Right Part From Yashvi Hydraulics
Send the model number stamped on your pump, valve or filter housing to Yashvi Hydraulics and we will confirm availability, price and lead time. If the plate is unreadable, send photographs of the unit and the machine it sits in and our team will identify it for you.
- Email: sales@yashvihydraulic.com
- Phone: +91 9560005194 / +91 9311203153
Yashvi Hydraulics supplies across India including Delhi NCR, Mumbai and West Bengal, and exports to Dubai, Abu Dhabi, the USA, Kenya, South Africa, Saudi Arabia and Russia.
