mRoy Metering Pump A vs B: Configuring a Continuous Chemical Dosing System

In a continuous dosing system, the worst thing a pump can do is stop every few weeks for a seal change. The mRoy metering pump A/B was built for exactly this. It uses a hydraulically balanced diaphragm with no dynamic seals and no plunger packing, and the brochure rates diaphragm life at up to 96000 hours. With routine servicing, year-round continuous running is realistic.

The model code is long, though, and first-time buyers often get stuck on A or B, which plunger, and which gear ratio. Work through those questions in order and the core of the dosing system falls into place.

Basic mRoy Metering Pump Specs

Inside an mRoy metering pump, a reciprocating plunger pushes hydraulic oil, and the oil moves a PTFE diaphragm that draws in and discharges the chemical, with accuracy within ±1%. Maximum rated flow per head:

• 50 Hz (1425 rpm): 1.1–330 L/h;
• 60 Hz (1725 rpm): 1.4–320 L/h.

The mRoy metering pump drive is an oil-bath worm gear in a fully sealed, dust-tight cast iron housing suitable for hazardous areas. An internal relief valve protects the hydraulic circuit, and the liquid end has a bleed system, which makes first start-up and restarts after service easier. Single or double heads are available, and the pump meets CE, ATEX and API675 requirements.

The chemical list is broad: coagulants, biocides, disinfectants, polymers, softeners, acids and alkalis for pH control, corrosion inhibitors and oxygen scavengers all appear in the brochure. By industry, it shows up in chemicals and petrochemicals, cooling towers and boilers, drinking water, oil and gas, food, pharmaceuticals and power.

Telling the mRoy A and B Frames Apart

The difference lies in plunger size and flow band. The figure after each plunger is the maximum pressure with a metal liquid end:

• A frame (MRA): C plunger 9.5 mm, 137.9 bar; D plunger 11.1 mm, 124.1 bar; E plunger 15.9 mm, 63.8 bar; F plunger 27 mm, 13.8–24.1 bar.
• B frame (MRB): K plunger 15.1 mm, 103.4 bar; L plunger 22.2 mm, 69 bar; R plunger 36.5 mm, 27.6 bar.

The A frame offers low flow at high pressure, suited to small doses into boilers and high-pressure lines. The B frame offers more flow, with the R plunger reaching about 330 L/h at 50 Hz, which suits high-consumption duties like cooling towers and wastewater.

A double-head B frame with the R plunger has a lower pressure limit still, flagged in a separate brochure note, so check double-head designs specifically.

Plastic Liquid Ends Are Rated Much Lower

Plenty of people see 137.9 bar and relax, but that's the metal liquid end figure. PVC and PVDF plastic liquid ends top out at 10.3 bar on both A and B frames. The table notes add that liquid ends used for fluoride dosing are rated the same way.

So in an mRoy metering pump dosing system, if the injection pressure is above 10 bar, you're essentially limited to metal liquid ends such as 316L, Alloy 20 or Hastelloy C.

Gear Ratio Sets the Stroke Rate

On an mRoy metering pump, the gear ratio code sets strokes per minute for a given plunger. At 50 Hz the A frame runs from 19 spm to 178 spm and the B frame from 40 spm to 148 spm. More strokes, more flow.

Fast strokes don't suit thick chemicals, though. The brochure includes a viscosity table: an A frame with the D plunger at the slowest gear ratio and a high-viscosity head can handle 8000 cP, while the same plunger at the fastest ratio handles only 350 cP. For viscous chemicals, choose a larger plunger at lower speed.

Options Derate the Flow

Several common mRoy metering pump options reduce actual flow, and the brochure gives adjustment factors:

• Electric or pneumatic stroke controller: ×0.95 for most plungers, ×1 for the K plunger, ×0.90 for L and R;
• Double-diaphragm rupture detection: ×0.95;
• High-viscosity option: ×0.75 to ×0.90, with smaller plungers losing more.

Each factor looks small alone, but stacked together they add up. Multiply them in and compare the result with your required dose, or you may find out the flow is short only after installation.

Reading the mRoy Metering Pump Model Code

The mRoy metering pump model is a string of codes in fixed order. Learn the order and quotes become easy to check:

Series (MRA or MRB) → number of heads (1 single, 2 double) → liquid end material → plunger diameter → gear ratio → motor or adapter → motor connection → suction/discharge connections → O-rings → flow adjustment → diaphragm rupture detection → base.

The liquid end material position alone offers 316L stainless, PVC, molded PVDF, machined PVDF, Alloy 20, Hastelloy C and more. Get that one position wrong and the whole pump is wrong. When an mRoy metering pump quote arrives, check it position by position in this order, especially plunger, gear ratio and liquid end.

Fitting an mRoy Metering Pump Into a Dosing System

Adjustment

Manual adjustment comes with a standard aluminum handle or a stainless one. For automatic control, there's the ACC electric stroke controller (waterproof or explosion-proof), or 0.2–1 bar pneumatic stroke adjustment.

Seals and connections

O-rings come in FKM, EPDM or Teflex. Connections are NPT threads or ANSI 1/2″ flanges in several ratings, chosen to match the piping design.

Diaphragm rupture detection

Pressure gauge and intermediate fluid types are available, with pressure switches in different protection ratings. Where the chemical is toxic or must not mix with hydraulic oil, fit it.

Conclusion

The mRoy metering pump A/B suits chemical dosing that has to run continuously for long periods. Choose A or B by flow and pressure, then plunger and gear ratio. Above 10.3 bar at the injection point, skip plastic liquid ends. For viscous chemicals, go large plunger and low speed. Finally, apply the flow factors for electric stroke control, double diaphragms and similar options. After those steps, the core equipment of the dosing system is essentially defined.

FAQ

Will the diaphragm really last 96000 hours?

That's the maximum life stated in the brochure. Actual life depends on chemical, temperature, pressure and maintenance, so stick to scheduled inspections.

Plastic or metal head for sodium hypochlorite on an mRoy metering pump?

It depends on pressure and concentration. Within 10.3 bar a plastic liquid end is an option. At higher pressure, confirm a suitable metal with the factory.

How do I calculate double-head mRoy metering pump flow?

The brochure tables show single-head flow, so double it for a double-head pump. A double-head B frame with the R plunger has a lower pressure limit.

No electrical control panel on site. Can flow still be automated?

Pneumatic stroke adjustment with a 0.2–1 bar signal is an option, provided there's a steady instrument air supply.

Does it need bleeding after a shutdown?

The liquid end has its own bleed system, so restarts are straightforward. After service, still confirm there's no trapped air in the head before putting it back on line.

If you're putting together a continuous dosing system, send us the chemical, dose and line pressure through our contact page and we'll check the mRoy plunger and gear ratio with you.