Milton Roy MaxRoy B: Where a Mechanical Diaphragm Pump With Built-In Relief Fits

The Milton Roy MaxRoy B deserves a look whenever flow sits between a few hundred and just over a thousand liters per hour and pressure stays at or below 10 bar. It is an oil-bath lubricated mechanical diaphragm metering pump. The literature lists maximum flow up to 1100 L/h, maximum pressure 10 bar, steady-state accuracy of ±1% across 10–100% of range, adjustment from 0 to 100%, suction lift of 2 m water column and maximum inlet pressure of 2 bar, and compliance with API 675. Compared with the G Series, its standout feature is a built-in relief valve that keeps the pump from running over pressure. Compared with hydraulic diaphragm pumps, it is simpler and easier to maintain. This guide is for engineers selecting pumps for water treatment, power and chemical projects.

Questions to answer before choosing the Milton Roy MaxRoy B

Four questions settle the product line before you look at model codes:

1. Maximum flow? A few liters per hour points to solenoid or small mechanical pumps. Hundreds to over a thousand L/h puts both the Milton Roy MaxRoy B and the G Series in range.
2. Discharge pressure? Up to 10 bar, a mechanical diaphragm pump can cover it. Above that, look at hydraulic diaphragm or plunger pumps.
3. Temperature and corrosiveness? These decide PVC or metal liquid end.
4. Is API 675 required? If so, the G Series is usually out.

Reading the Milton Roy MaxRoy B data

The MaxRoy B145 in the literature has a 145 mm diaphragm and four stroke speeds:

• 58 spm, 1/25 ratio, about 363 L/h
• 96 spm, 1/15 ratio, about 621 L/h
• 144 spm, 1/10 ratio, about 860 L/h
• 180 spm, 1/8 ratio, about 1051 L/h

Those flows are at 10 bar and are the same for PVC and metal liquid ends. Stroke speeds assume a 1440 rpm motor. A 60 Hz motor raises flow by 20%, but do not use a 60 Hz motor on the 180 spm version. Motor codes cover 0.75, 1.1 and 1.5 kW, three-phase 380 V, IP55, class F insulation.

Lubricant is ISO VG 150 or equivalent, about 4 L.

What the built-in relief valve does

The internal relief valve prevents the pump from operating above its pressure limit. A closed discharge valve, a crystallized injection valve or a blocked line all make discharge pressure climb. If the external relief valve is in the wrong place, set too high or missing, the head and piping are at risk.

Building relief into the Milton Roy MaxRoy B gives the pump its own protection, which is useful on sites where piping changes often or supervision is light. It does not replace the system relief valve, and the discharge line should still have one as the design code requires.

Diaphragm life and double diaphragm option

For the Milton Roy MaxRoy B, the literature states that the PTFE and elastomer composite diaphragm typically reaches about 20,000 hours, varying with the liquid and operating conditions. Single or double diaphragm construction is available, and the double version can carry rupture detection for toxic, aggressive or zero-leak duties.

Choosing a liquid end

Two standard liquid ends are offered:

• PVC: PVC head, valve body and disc, PE seats, glass balls, PTFE diaphragm, Viton seals. The PVC liquid end is rated 10 bar at 20 ℃, losing 1.1 bar of pressure rating for every 5 ℃ rise, with a 50 ℃ maximum.
• 316 SS: 316 head, body, seats and balls, PTFE diaphragm and seals, with liquid temperature up to 90 ℃.

Special builds include concentrated sulfuric acid (316 SS liquid end, 904L seats, Hastelloy C balls), spring-loaded 316 SS balls for high viscosity and 440C balls and seats for slurries.

Where the Milton Roy MaxRoy B fits

Good fits:

1. Municipal water treatment feeding hypochlorite, PAC, acid or caustic at a few hundred L/h.
2. Power plant boiler water treatment and industrial water and wastewater injection points at or below 10 bar.
3. Petrochemical, chemical and refinery process injection where pressure is moderate and API 675 is specified.

Poor fits:

• Duties above 10 bar such as drum dosing or high-pressure line injection, where Milroyal or Primeroyal hydraulic diaphragm and plunger pumps belong.
• Very small feeds of a few to a few dozen L/h, where solenoid or small mechanical pumps are more economical.
• Liquids above 50 ℃ on a PVC liquid end; switch to metal.

Options that change the price

Cost on the Milton Roy MaxRoy B is driven by liquid end material, motor power and explosion protection, single or double diaphragm with rupture detection, electric or pneumatic actuators or variable speed, multiplex heads, flanged or sanitary connections and a stroke counter. Settle the duty first and then confirm each option, so quotes can be compared fairly.

Installation and maintenance notes

On a Milton Roy MaxRoy B, check the oil level before first start and change oil on the manual's schedule. Keep suction flooded or short; the 2 m lift figure excludes viscous liquids. Add back pressure valves and pulsation dampeners as needed, and recheck the PVC pressure rating in hot weather. Stop, isolate and release pressure before maintenance.

Conclusion

The Milton Roy MaxRoy B suits medium flows up to 1100 L/h at up to 10 bar, with a built-in relief valve and API 675 compliance as its strengths. Pick PVC or 316 SS by temperature and chemical. Go hydraulic diaphragm for higher pressure and solenoid for very small flows. Compare with the Milton Roy model guide, G Series GM and GB selection and the MaxRoy B product page, and see the Milton Roy brand page. Send flow, pressure, chemical and temperature and contact our engineers.

FAQ

MaxRoy B or G Series?

Both are mechanical diaphragm pumps. Choose the MaxRoy B when you need the internal relief valve, API 675 or higher flow; the G Series covers most routine water treatment.

Can the Milton Roy MaxRoy B run on 60 Hz?

Yes, with 20% more flow, but not on the 180 spm version.

What should I watch with a PVC liquid end in summer?

Pressure rating falls 1.1 bar for every 5 ℃ rise, up to 50 ℃ maximum, so check discharge pressure against actual temperature.

Does the internal relief valve replace a system relief valve?

No. It protects the pump; the discharge line still needs a relief valve per the design.

Which oil does it use?

ISO VG 150 or equivalent, about 4 L, changed at the interval in the manual.