Valveless Metering Pump Selection Guide: FOREACH Models and Applications
To select a valveless metering pump, first define the volume per dose and the time available for dispensing. Then check displacement per revolution, drive speed, wetted materials, backpressure and connections, and verify delivery in the actual fluid path. Neither flow rate alone nor the label ‘metering pump’ is enough to select a model.
Using the FOREACH RPL-P4, RPL-P6.35 and RPL-P15 single-head valveless metering pumps, this guide explains how to turn reagent dispensing, titrant delivery and repeat filling requirements into selection criteria that can be compared and tested.
01Which parameters matter when selecting a valveless metering pump?
Write down how much liquid is needed per operation and how much time the pump has before comparing specifications. The same dose volume can place different demands on the drive and fluid path in repetitive filling, intermittent dispensing and incremental titration.
Distinguish displacement per revolution, dose volume and average flow rate
| Parameter | Meaning and unit | What to check |
|---|---|---|
| Displacement per revolution | Nominal volume delivered during one complete rotational cycle at the current displacement setting, in μL/rev. | Volume per revolution and the number of revolutions required. |
| Dose volume | Volume to be delivered into the container in one operation, in μL or mL. | How much liquid the equipment needs each time. |
| Average flow rate | Average volume delivered per unit of time, in μL/min or mL/min. | Whether delivery can be completed within the time allocated to the pump. |
For a nominal estimate at fixed displacement using complete cycles, dose volume depends on displacement per revolution and the number of revolutions. Speed mainly determines the time needed to complete those cycles. An average flow rate does not imply a constant instantaneous flow.
Dose volume = displacement per revolution × number of revolutions
Average flow rate = displacement per revolution × rotational speed
Use consistent volume units in both equations. These are nominal estimates for complete cycles, not evidence that delivery through arbitrary small rotation angles has been validated.
Example: what flow rate is needed to dispense 1 mL in 2 seconds?
If the pump has 2 seconds of net dispensing time to deliver 1 mL, the required average flow rate during delivery is:
1 mL ÷ 2 s × 60 s/min = 30 mL/min
This converts an equipment requirement; it is not a measured capability of a particular model. If a station completes a cycle every 2 seconds but also needs time for bottle indexing, needle movement or measurement, the pump has less time available. Subtract these intervals before recalculating.
Check wetted materials, connections and cleaning
List the composition, concentration and temperature of the working liquid and cleaning fluid. Then check all wetted components, including the pump head, ceramic parts, fittings and tubing. The pump-head material alone cannot establish compatibility of the complete fluid path. For liquids prone to crystallization or residue, also define the flushing procedure after shutdown.
Beyond thread specifications, check connection type, tube diameter and installation space. Working ports and cleaning ports serve different purposes. Connect tubing according to the configuration drawing rather than treating ports with the same thread as interchangeable.
Include backpressure, inlet conditions and the drive
Record inlet liquid level, suction height, tubing length and internal diameter, and outlet restrictions such as needles and filters. For the drive, confirm the available speed range, start/stop behavior and positioning method. Whether the pump can deliver the required average flow must be verified under these conditions.
Pressure rating and accuracy test conditions are not the same. For example, the current English specification sheet for RPL-P6.35 and RPL-P15 uses pure water, lists a liquid-pressure condition of no more than 50 kPa, and specifies test speeds of 100 rpm and 300 rpm respectively. Those results are not a delivery guarantee for every reagent and backpressure.
02How do RPL-P4, RPL-P6.35 and RPL-P15 compare?
Start with displacement per revolution, then narrow the options by dispensing time, materials and connections. A larger displacement is not automatically suitable for every small-dose task. The same target volume may be delivered using different combinations of displacement and revolutions.
| Specification | RPL-P4 | RPL-P6.35 | RPL-P15 |
|---|---|---|---|
| Displacement per revolution | 12–80 μL/rev | 50–300 μL/rev | 300–1200 μL/rev |
| Speed range | 5–300 rpm | 5–300 rpm | 5–300 rpm |
| Pump-head material | Polyvinylidene fluoride (PVDF) | Polyvinylidene fluoride (PVDF) | Polyvinylidene fluoride (PVDF) |
| Working-fluid connections | 1/4-28 UNF-2B | 1/4-28 UNF-2B | G1/8 |
Sources: RPL-P4 product information and the current English specification sheet for RPL-P6.35 and RPL-P15. These ranges support initial screening; the actual displacement setting and connection configuration must match the selected product.
For small doses, start with the target volume—not the lower displacement limit
RPL-P4 has a smaller displacement-per-revolution range and can be evaluated for small-volume reagent addition, titration increments or repeated dispensing. However, 12 μL/rev is the lower end of its displacement range, not a validated minimum reliable dose. As the target volume decreases, drive positioning, tubing compliance, bubbles and residual liquid at the needle tip become increasingly important to the volume actually delivered.
For larger doses, compare both revolutions and completion time
RPL-P6.35 and RPL-P15 cover different displacement ranges. For a given target volume, estimate nominal running time from the available displacement and speed, then compare actual start/stop behavior and the process of droplets entering the container. More volume per revolution does not by itself mean a faster overall filling cycle.
The current specification sheet lists standard displacements of 50, 100, 200 and 300 μL for RPL-P6.35, and 400, 800, 1000 and 1200 μL for RPL-P15. It also allows non-standard configurations within each range. A value falling within the listed range therefore does not mean the supplied configuration is already set to that displacement.
Materials and ports may determine the final choice
RPL-P6.35 uses zirconium dioxide (ZrO₂) ceramic parts, while RPL-P15 uses aluminum oxide (Al₂O₃). Their working connections are 1/4-28 UNF-2B and G1/8 respectively; both list 1/4-28 UNF-2B cleaning connections. Even when volume and time requirements are met, reagent compatibility, cleaning arrangements and tubing connections still need checking.
03How do selection priorities differ for dispensing, titration and filling?
‘Valveless metering pump’ describes the pump mechanism and function, while ‘reagent dispensing pump’, ‘titrant dosing pump’ and ‘liquid filling pump’ describe its task in the equipment. The same mechanism can serve different tasks, and a given task may use other pump mechanisms. FMI’s explanation of dispensing versus metering and IWAKI’s naming of the VMP illustrate this application-based terminology.
| Industry or equipment context | Names you may encounter | Confirm first |
|---|---|---|
| Automated analytical instruments and sample preparation equipment | Reagent dispensing pump; reagent dosing pump | Reagent volume per dose, available time and first dose after a pause. |
| Automatic titrators and laboratory titration systems | Titrant dosing pump; titrant delivery pump | Smallest target increment, dosing intervals, mixing and reading delays. |
| Reagent filling equipment and small-container filling stations | Reagent filling pump; aliquoting pump | Fill volume per container, consistency, indexing and droplet-release time. |
| Continuous liquid-feed modules in instruments | Liquid metering pump; controlled liquid-feed pump | Operating flow, duration, backpressure and allowable flow fluctuation. |
Reagent dispensing: measure what actually enters the reaction vessel
Specify both target volume and delivery window for a reaction cup. For intermittent operation, test continuous dispensing and the first dose after a pause separately. Collect liquid at the actual needle outlet, maintaining the normal installation height and fluid-path resistance. Measuring only at the pump port may overlook residual droplets, wall adhesion or bubbles.
Titrant delivery: check increments, response and reading sequence
Near the titration endpoint, the instrument may need smaller additions. List the target increments for coarse and fine dosing, then test the actual output per command, start/stop response and droplet detachment. Allow separate time for mixing stabilization and measurement. The pump delivers liquid; the instrument’s detection and control system determines the endpoint.
Quantitative filling: assess the complete cycle, not just pump running time
Once fill volume is defined, include container indexing, needle movement, droplet detachment and necessary delays in the cycle-time plan. For foaming or wall-wetting liquids, check that the entire dose enters the container as well as weighing it. To assess fill consistency, keep the outlet position and collection method fixed and include real operating pauses and restarts.
Continuous feed: check cumulative volume and flow fluctuation
In addition to average flow, define the fluctuations acceptable downstream. Testing should cover the expected operating duration and changes in inlet liquid level and outlet resistance. If the process is sensitive to instantaneous flow, ask the supplier to assess that requirement explicitly; average flow cannot substitute for it.
04How should actual dispensing performance be verified?
The objective is to confirm that liquid reaches the target container as required under the actual fluid-path and cycle conditions. Calculations narrow the shortlist; prototype testing confirms the configuration. Record results in the following order rather than relying on a single collection.
Fix the liquid and fluid-path conditions, then prime and remove air
Record liquid composition, concentration and temperature; inlet level; tubing length and internal diameter; needle specification; outlet backpressure; displacement setting; and drive program. Check fitting seals and prime the path to the outlet with the working liquid before measuring.
Calculate mean deviation and repeatability separately
Make multiple independent collections at the same setting and record each result. Mean deviation shows how far average delivery is from the target; repeatability shows how closely repeated outputs cluster. A mean close to the target does not imply that every dose is close to it.
For gravimetric measurement, subtract container mass and convert liquid mass to volume using density at the test temperature. Check whether balance resolution, evaporation and handling time materially affect the result.
Record the first dose after a pause separately
Resume dispensing after the equipment’s actual pause duration and record the first dose separately from subsequent continuous doses. This can reveal retraction, residual droplets, bubbles or first-dose deviations that occur only after a pause, instead of hiding them in the average during continuous operation.
Retest with the complete cycle and expected boundary conditions
Restore bottle indexing, needle movement, mixing and measurement delays to the sequence. Cover expected changes in inlet level, temperature and outlet resistance. Record actual liquid-arrival time and full cycle time to confirm that volume and throughput requirements can both be met.
| Observation | Check first | Next step |
|---|---|---|
| Repeated deviations tend in the same direction | Setpoint, unit conversion, displacement calibration and liquid density. | Recheck mean output after verifying these factors. |
| Individual doses vary substantially | Bubbles, liquid supply, fitting seals and needle-tip droplets. | Fix conditions, investigate one factor at a time and retest. |
| Continuous dosing is normal, but the first dose after a pause is not | Retraction during shutdown, residual liquid, dripping and pause duration. | Reproduce the pause and record the first dose separately. |
These observations guide the order of checks; none identifies a fault cause on its own. Agree the sample count, allowable deviation and repeatability criterion before testing.
05Frequently asked questions about valveless metering pump selection
Does reducing speed reduce the volume of each dose?
If displacement and the number of complete revolutions stay the same, lower speed mainly increases dispensing time; nominal dose volume stays unchanged. With fixed-duration control, speed changes affect accumulated revolutions and delivered volume, so recalibration is needed.
Is the lower displacement limit the minimum dose volume?
No. The lower displacement limit is a nominal output parameter for a complete rotational cycle. The minimum reliable dose also depends on drive positioning, liquid, tubing and needle-tip conditions, and should be measured under the target operating conditions.
Does a polyvinylidene fluoride pump head suit every reagent?
The pump head is only one part of the assessment. Check ceramic parts, fittings, tubing and all other wetted components individually, considering the composition, concentration, temperature and contact time of both the reagent and cleaning fluid.
Does a valveless design mean the equipment needs no valves at all?
No. RPL combines rotary and reciprocating motion of a ceramic piston to draw in and discharge liquid without valves in the pumping mechanism. Whether the complete instrument needs switching valves, isolation valves or other fluid-path components depends on its supply, cleaning and safety-control design.
Can one single-head RPL pump proportion two liquids independently?
A single-head pump alone cannot independently control the volume ratio of two fluid paths. Assess a second path, the control method or a DRPL dual-head configuration separately, and confirm downstream combining and mixing requirements.