Salt crystallisation in dosing pumps: the silent killer of your instrument
Why concentrated salt solutions wreck piston pumps, and what you can do about it
Salt crystallisation in dosing pumps is the most underestimated cause of failure in diagnostic and analytical instruments. The pump runs without problems for months, the dosing volumes remain within specification, and then the instrument suddenly starts showing inexplicable deviations. Shortly afterwards, leakage follows and the instrument comes to a standstill.
What happened in the meantime has been invisible. Microscopic amounts of salt solution have seeped past the seal, dried into crystals and gradually abraded that seal. By the time you notice the problem, the damage is already irreparable.
This article explains exactly how this failure mechanism works, why the common solution (flushing) introduces more risk than it removes, and which material technology tackles the problem at its source.
⏱ approx. 8 minutes reading time
How salt crystallisation destroys a dosing pump
The failure mechanism proceeds in four steps. Each step on its own seems harmless; together they form an inevitable degradation cycle.
1. Liquid passes the seal
With every stroke of the piston, a minuscule volume of liquid remains on the piston surface as it moves through the seal. This is inherent in the principle: a seal that wipes completely dry would cause unacceptable friction and wear.
2. The liquid evaporates
On the back of the seal, the remaining moisture is exposed to air. The water evaporates and leaves the dissolved salts behind. With concentrated solutions, this happens quickly: every stroke adds a new layer.
3. Salt crystals adhere to the piston
The remaining salts crystallise and adhere to the piston surface. On conventional materials such as ceramics, these crystals stay in place. They continue to grow with every cycle.
4. The crystals abrade the seal
On the next stroke, the piston with the adhering crystals passes back through the seal. The crystals act as an abrasive and cut grooves in the sealing material. These grooves form leak paths. From that moment on, the problem increases exponentially: more leakage means more liquid behind the seal, which means more crystals.
The result is catastrophic failure
With traditional piston pumps, concentrated salt solutions lead to complete failure relatively quickly. By way of illustration: a conventional ceramic piston pump pumping 10 percent NaOH already shows clearly visible salt deposits around the seal and incipient wear after approximately 1 million cycles.
Where do you encounter concentrated salt solutions?
The problem is more widespread than many instrument manufacturers realise. As soon as a reagent or buffer contains a significant salt concentration, the mechanism is active.
| Field of application | Typical media | Risk level |
| In vitro diagnostics (IVD) | Reagents, buffers, wash solutions with high ionic strength | High. Continuous operation, critical accuracy |
| Clinical chemistry analysers | Physiological saline, reagent buffers | High. Large numbers of cycles per day |
| Haematology | Diluents, lysis reagents | High |
| Cleaning and decontamination | NaOH solutions, hypochlorite | Very high. Often the most aggressive step in the system |
| Molecular diagnostics | Extraction buffers with a high salt concentration | High |
| Environmental and water analysis | Calibration and standard solutions | Medium to high |
| Industrial process analysis | Process samples with dissolved salts | Variable, depending on the matrix |
Why flushing is not a solution
The common response to this problem is to install a flushing facility behind the seal. A continuous or periodic flow of water or buffer is intended to rinse away the salt residues before they can crystallise. In practice, this approach introduces three new problems.
Risk 1: contamination of samples and reagents
A second fluid path is created that physically adjoins the primary path. In the event of wear or pressure differences, flushing liquid can enter the sample path, or vice versa. In diagnostic applications with carry-over requirements, this is a direct quality risk that is difficult to detect.
Risk 2: exothermic reactions
When flushing liquid comes into contact with certain reagents, exothermic reactions can occur. In an enclosed space inside an instrument, this is a safety risk, not just a technical problem. Think of the combination of concentrated alkali and acid, or of reagents that react violently with water.
Risk 3: additional complexity and points of failure
A flushing system means extra tubing, an extra pump or pressure source, extra valves, extra waste drainage and extra software to control everything. Each of these components is a potential point of failure and requires maintenance. The solution to one problem creates a chain of new ones.
The conclusion from practice
Flushing behind the seal does extend the service life, but it entails considerable risks for the instrument. Contamination of samples and reagents is likely and there is a chance of exothermic reactions. This common practice is best avoided.
The material solution: breaking the mechanism at its source
If flushing treats the symptom, the question is: can the underlying mechanism be eliminated? It can, by designing the piston surface in such a way that the two critical steps in the degradation cycle no longer occur.
Point of intervention 1: superhydrophobicity
A highly water-repellent piston surface ensures that less liquid remains behind as the piston moves through the seal. The liquid simply does not adhere to the surface and is repelled instead.
Less liquid behind the seal means less salt deposition.
With the Maestro ULTRA, Bio-Chem Fluidics has created the most hydrophobic piston on the market today. This keeps the amount of liquid that passes the seal to a minimum.
Point of intervention 2: low surface energy
Completely preventing liquid from remaining behind is physically impossible. The second line of defence is therefore to ensure that any crystals that do form do not adhere.
A surface with very low surface energy offers materials nothing to grip onto. Salt crystals left behind by evaporating liquid do not adhere to the piston but flake off and fall away. The piston surface therefore remains as smooth as on the day it was made.
No crystals means no wear of the seal, and therefore no leakage
The demonstrable difference
Whereas a conventional ceramic piston pump shows clear salt deposits and incipient seal wear after approximately 1 million cycles with 10 percent NaOH, a piston with superhydrophobic and low-energy properties is still free of crystal deposits after 3 million cycles with the same medium. Three times as many cycles, without degradation.
What this means for your instrument design
Eliminating salt crystallisation as a failure mechanism has consequences that reach beyond the pump itself. For OEM instrument manufacturers, it changes the design space.
| Aspect | With flushing system | No flushing system needed |
| Fluidic design | Second fluid path, extra valves and drainage | Single path, fewer components |
| Points of failure | Every extra component is a risk | Fewer components, higher reliability |
| Software | Control of flushing cycles and timing | Simplified control logic |
| Maintenance | Periodic inspection and replacement | Designed to be maintenance-free |
| Instrument uptime | Interruptions for flushing and service | Higher availability |
| Contamination risk | Present due to the second fluid path | Eliminated |
| Time-to-market | Development time for the flushing system | Shorter development cycle |
| Total cost of ownership | Service costs and consumables | Lower life-cycle costs |
The Maestro series from Bio-Chem Fluidics
The Maestro plunger pumps have been developed for applications in which accuracy and service life are both critical. They have been designed and validated to offer a service life twice as long as that of comparable dosing pumps on the market, and are ideally suited to IVD and similar low-pressure applications.
| Specification | Value |
| Dosing volumes | 100, 250, 500, 1,000, 2,500 and 5,000 microlitres |
| Accuracy | Programmable up to 100 percent |
| Precision | Less than 0.2 percent CV |
| Full stroke | 12.7 mm |
| Optional valve | Integrated 3-way valve |
| Communication | RS-232, RS-485 or CAN |
| Integration | Manifold integration possible |
The Maestro ULTRA adds the patented piston technology that is completely immune to the negative effects of salt crystallisation. For instruments that handle concentrated salt solutions, this removes the dominant failure mechanism from the equation.
Manifold integration for OEM applications
For systems with multiple dosing channels, Maestro pumps can be mounted on a customer-specific manifold and supplied as an assembled subsystem. This lowers assembly costs on your side and guarantees the compatibility of the whole.
Do you recognise these signals in your instrument?
Salt crystallisation announces itself before the pump finally fails. Look out for the following signals:
- Dosing volumes that gradually deviate from the calibration value for no apparent reason
- Increasing variation between successive doses (rising CV)
- Visible white or crystalline deposits around the piston or the seal area
- Traces of moisture or droplets at the back of the pump head
- Pumps in the same instrument that structurally last shorter than expected
- A service history in which the same pump position has been replaced repeatedly
The last signal is the most revealing. When one specific pump position in your instrument fails time and again while other positions run without problems, the cause almost always lies in the medium that pump handles, not in the pump itself.
Frequently asked questions about salt crystallisation in dosing pumps
At what salt concentration does this problem start?
There is no sharp threshold. The mechanism occurs as soon as dissolved salts are present and the liquid behind the seal can evaporate. The higher the concentration and the higher the cycle frequency, the faster the degradation. With concentrated solutions such as 10 percent NaOH, degradation is measurable within a few months of continuous operation.
Does it help to flush the pump with water after use?
A cleaning cycle through the normal fluid path removes salt residues from the pump chamber, but does not reach the zone behind the seal where the problem occurs. For that zone, flushing is only possible via a separate flushing path, with the associated risks of contamination and exothermic reactions.
Isn't a ceramic piston actually very wear-resistant?
Ceramics are indeed very hard and wear-resistant. But that is not where the problem lies. The piston does not wear; the seal wears, because salt crystals adhering to the ceramic piston act as an abrasive. The hardness of the piston does not solve that. The solution lies in preventing adhesion, not in harder materials.
What is the difference between the Maestro and the Maestro ULTRA?
The Maestro series is the baseline, with programmable accuracy, precision below 0.2 percent CV and a service life twice that of comparable dosing pumps. The ULTRA adds the patented piston technology with superhydrophobicity and low surface energy, specifically aimed at immunity to salt crystallisation.
Can I replace an existing pump without redesigning my instrument?
That depends on the mechanical and fluidic interface of your current set-up. In many cases, replacement is possible within the existing design, especially when the dosing volumes and connections match. If a flushing system can be dispensed with, this also frees up space in the design. Submit your configuration to a specialist for a concrete assessment.
