Anyone who has used an SLA or DLP resin printer knows that familiar dilemma: the resin in the vat is running low, but the print is still going. Do you pause the machine to top it up, or gamble that it finishes before the resin runs dry? Pause the print, and you'll almost certainly end up with a visible layer line right where the print stopped-the whole model is essentially ruined. Let it run, and once the resin runs out, the print head may drag across an empty vat, potentially scratching the FEP film or the build plate itself. Either way, it's not a great outcome.
And that's not even mentioning the mess of manually adding resin. Resin has a noticeable smell, and a slight tremor in your hand while pouring can send a stream of sticky liquid onto the printer's surface, which is a pain to clean up. For small print shops running multiple machines, the constant need to monitor and refill resin throughout the day is a genuine drain on productivity and focus.
Fortunately, there's a straightforward fix. A compact peristaltic pump paired with a simple level sensor can automate the entire refill process. The system monitors the resin level and adds a small amount whenever it drops below a set point-no human intervention required. The whole setup is inexpensive, and the improvement in day-to-day usability is substantial. Below, I'll walk through why this works, how to choose the right pump, and the practical steps to build your own system.
Why Manual Resin Refilling Is More Annoying Than It Seems
Let's break down exactly why automating this step is worth the small effort:
Pausing a print is often a death sentence. A typical resin print runs for several hours, sometimes over ten. If you have to pause it mid-way to add resin, the cured layer at the pause point often shows a visible seam or stress line. For detailed models or functional parts, this often means scrapping the piece and starting over.
Spilled resin is a sticky mess. Resin isn't like water-it doesn't wipe off cleanly. Spills leave a tacky film that collects dust and looks terrible. If resin drips onto the LCD screen or the Z-axis rail, it can interfere with print accuracy or even damage components.
For small businesses, it's pure time theft. Every time you need to hover over a machine to add resin, you're not doing something more productive. In a workshop with several printers, the cumulative time spent on manual refills adds up quickly.
Overnight and unattended printing is nearly impossible. A standard 1–2 litre resin vat may not last through a long night print. When the resin runs out at 3 a.m., the machine sits idle, wasting time and electricity-and you wake up to a failed print. Anyone who's experienced that knows the frustration.
Why a Peristaltic Pump Is the Best Choice for Pumping Resin
Several types of small pumps exist-centrifugal, diaphragm, gear, and peristaltic-but for resin dispensing, peristaltic pumps offer distinct advantages that make them the clear winner.
Resin touches only the inside of the tube. This is the defining feature of a peristaltic pump. The resin never contacts any metal or plastic pump parts; it flows entirely within a flexible tube. Photopolymer resins can be chemically aggressive, and prolonged contact with certain materials may cause degradation or leaching of contaminants. With a peristaltic pump, that concern disappears. Replacing the tube costs pennies and effectively gives you a new fluid path.
Great self-priming capability. Peristaltic pumps are positive-displacement pumps, so they can generate enough suction to pull resin up from a bottle without needing to be pre-filled with liquid. Just drop the intake tube into your resin container, and the pump will draw it up. This is far simpler than centrifugal pumps, which often need to be primed manually.
Handles varying resin viscosities well. Different resins have very different viscosities-some engineering resins are as thick as honey. Peristaltic pumps move fluid by squeezing the tube, so viscosity affects flow rate but rarely causes the pump to stall. As long as the tube isn't completely blocked, the pump keeps working.
Maintenance is remarkably simple. The only component that wears out is the tube. Replacing it takes less than two minutes. If a gear pump or diaphragm pump gets clogged with cured resin particles, cleaning it is a messy, time-consuming job. With a peristaltic pump, you simply swap in a new tube.
Flow control is linear. Peristaltic pump flow rate is directly proportional to motor speed, making it easy to control accurately. When paired with a level sensor and a simple control circuit, you can achieve precise, repeatable refills-no overfilling, no underfilling.
What You Need to Build an Automatic Refill System
The components are simple, and the build is easier than most people expect:
A peristaltic pump. Look for a small pump with a flow rate around 100–300 mL/min. Refills are typically only tens of millilitres and take just a few seconds. If the pump is too fast, controlling the exact amount becomes trickier. A moderate flow rate with resin-compatible tubing is the sweet spot.
A level sensor. This detects the resin level in the vat. Photoelectric sensors are the most accurate and don't contact the resin, so they stay clean. Capacitive sensors can work but may need a protective coating. Float switches are simple but have moving parts that can stick in viscous resin. For most users, a non-contact photoelectric sensor is the easiest and most reliable choice.
A reservoir bottle. Use an opaque container-amber or dark glass works well to protect the resin from light. Drill two holes in the lid: one for the pickup tube that reaches to the bottom, and another for an air vent to equalise pressure. Placing the reservoir slightly above the vat can use gravity to assist flow, but beware of siphoning.
A controller. An Arduino or Raspberry Pi Pico with a few lines of code can read the sensor and switch the pump on and off. If your printer's mainboard has spare I/O, you can also integrate the system directly, triggering refills via G-code or printer scripts.
Tubing and fittings. Use 4mm or 6mm ID silicone or PTFE tubing. Connect the pump's included tubing to the rest of the loop using a suitable reducer. Keep tubing runs as short and straight as possible to minimise resistance.
Key Selection Criteria for the Pump
If you're sourcing components yourself, pay attention to these factors:
Tubing compatibility with resin. This is the most important consideration. Photopolymer resins contain various monomers and sometimes solvents. Ordinary silicone tubing may swell, harden, or crack after prolonged exposure. Look for tubing with good chemical resistance, such as PharMed, Tygon, or PTFE-these are formulated to handle aggressive fluids.
Flow rate. SLA vats typically hold a few hundred millilitres to about a litre. A refill of 50–100 mL is usually plenty, so a pump rated at 100–300 mL/min works well. If you're looking at a pump rated at 20–50 mL/min (common for cooling applications), it may still work but will refill more slowly-fine for smaller vats or patient users.
Voltage and power. Most small peristaltic pumps run on 12V DC. You can power them from a separate adapter or tap into your printer's power supply. If using the printer's board, confirm that the output can handle the pump's start-up current, which can be higher than its running current.
Noise. Peristaltic pump noise comes mainly from the motor and roller mechanism. Good-quality pumps with smooth bearings are fairly quiet. Since the pump only runs for a few seconds at a time, noise is less critical than in a cooling system, but a quieter pump is always nicer if your printer is in a living or workspace.
Practical Installation Tips
The system is conceptually simple, but a few installation details can make the difference between rock-solid reliability and constant fiddling:
Mount the level sensor at the right height. Install it on the side of the vat, about one‑third to half‑way up from the bottom. Too high, and the pump will trigger too frequently. Too low, and the resin gets dangerously low before a refill is triggered. Test the trigger point with a small amount of resin before running a full print.
Place the reservoir lower than you might think. Counter‑intuitively, if you place the reservoir above the vat, resin will tend to siphon through the tubing even when the pump is off, leading to overfilling. Keep the reservoir at roughly the same height as the vat, or slightly lower, and avoid downward slopes in the tubing that could encourage siphoning.
Keep the tubing path smooth. Minimise bends and kinks, especially right before and after the pump head. If bends are unavoidable, use large-radius curves instead of sharp angles, which restrict flow and stress the pump.
Test with distilled water first. Before loading resin, run distilled water through the system to check for leaks, confirm the pump works correctly, and verify the sensor logic. Water is thinner than resin, so if the system works with water, it will almost certainly work with resin.
Top up the reservoir before it runs dry. Don't wait until the reservoir is completely empty to refill it. If air gets drawn into the line, the pump may need to re-prime, which can take a few seconds and lead to inconsistent refills. Make a habit of checking the reservoir before starting a long print.
Who Benefits Most from This Setup?
Casual hobbyists. If you only print occasionally, manual refilling might not seem like a big deal. But the modest cost and effort of building an auto-refill system can still make each print much more enjoyable.
Small print shops with multiple machines. This is where automation really shines. The time saved per machine adds up across three, four, or five printers. Freeing yourself from constant monitoring lets you focus on post‑processing, customer orders, and other value‑added work. Overnight and weekend prints become viable, boosting overall throughput.
Users printing large models. Big prints take a long time and consume a lot of resin. The risk of a mid‑print resin shortage is much higher, and the cost of failure is greater. An auto‑refill system is almost essential for these jobs.
Frequently Asked Questions
Q: Will the tubing degrade in resin over time?
Yes, tubing is a consumable. Under regular use, good-quality tubing can last several months to a year. Inspect the section that contacts the rollers-if the tubing appears flattened, feels soft, or shows surface cracks, replace it. Replacement tubing is inexpensive, so keep a spare on hand.
Q: What if resin cures inside the tubing?
If the system sits idle for a long time, residual resin in the tubing may cure. To prevent this, flush the tubing with IPA (isopropyl alcohol) or a dedicated cleaning solution before extended downtime. If the tubing is already blocked, replace it-it's easier than trying to clear cured resin.
Q: Can one system handle two types of resin?
Technically you can run two separate pumps and tubing sets for different resins, but sharing a reservoir risks cross‑contamination, which can affect curing properties. It's safer to keep one pump and reservoir per resin type.
Q: Will the sensor get fouled by resin over time?
Non-contact photoelectric sensors don't touch the resin, so fouling isn't an issue. Contact‑type sensors may accumulate a film of resin that affects sensitivity. For this reason, photoelectric sensors are the preferred choice.
Final Thoughts
Resin refilling on an SLA printer might seem like a minor inconvenience, but over time, the interruptions and mess add up to more frustration than you'd expect.
A peristaltic pump offers a simple, low‑cost, and low‑maintenance solution. Resin contacts only the tubing, so there's no concern about corrosion or contamination. Self‑priming capability means you don't have to pre‑fill the pump-just drop the tube in and go. Linear flow control, paired with a level sensor, delivers precise, reliable refills.
Once you've used an auto‑refill system for a while, the biggest difference is peace of mind. The machine looks after itself, and you're free to focus on the actual printing.
For detailed specifications on suitable peristaltic pumps, check our product pages. And if you run into any issues during installation, our technical support team is happy to help.