339-0047-000 8/00 mRoy A and B - Milton Roy Company - #19

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The installation of an external Safety Valve is recom-mended, since the pump’s internal relief valve is not in-tended to protect the piping system. Refer to “Settingthe Relief Valve” in Section 3, for further relief valvediscussion. (Milton Roy offers a complete line of backpressure and safety valves).For satisfactory metering and capacity control, the dis-charge pressure at the pump must be 50 PSIG (3.5Bar) Minimum for the mRoy A and 70 PSIG (4.8 Bar) minimum for the mRoy B. Therefore, when the pump is to discharge into an open system, a back pressuredevice must be installed in the pump discharge car-tridge or line. (except the mRoy A plastic design). Installation of this spring will assure repetitive metering accuracy. A spring (1390) is attached to each pump (Metallic Liq-uid End) in a small cloth bag (1380) for installation inthe discharge cartridge to develop the required backpressure on the pump if a separate back pressurevalve is not used (mRoy A Figure 15 and 21, mRoy B Figure 25). The back pressure spring should slip easilythrough the hole in the seat. Do not disassemble theseat and/or ball from metallic check valves. These check valves are precision manufactured at Milton Royand should not be disassembled in the field. Discharge Piping NOTE: Many pipe joint compounds are not suit-able for use with plastic pipe and, if used, will cause stress cracking at the connection. Use onlycompounds commended for use with plastic mate-rials. Suction Piping The suction piping must be absolutely tight and leak-free. For mRoy pumps on water-like solutions we rec-ommend that the suction pipe be ¾” minimum diameter and a maximum of 6 feet (2 meters) long. The intent is that the piping must be designed to provide an ade-quate net positive suction head (NPSH). Obtain ourNPSH Calculation software at the Milton Roy Web site (miltonroy.com). If assistance in determining NPSH isneeded, contact the Milton Roy Aftermarket Servicedepartment.A flooded suction is recommended for optimum servicelife and maintenance-free operation. However, themRoy pump can operate with less than flooded suction if necessary, in accordance with the following schedule shown in the chart below. Refer to “Installation with Suction Lift,” which outlineslimiting conditions if suction lift requirements are antici- pated.The supply tank should incorporate a low-level switchto cut off the pump motor circuit before the suction intake is exposed to air. Otherwise, the pump mayoccasionally run dry. Figure 15. Back Pressure Spring Installation Model NumberMin. NPSH (PSIA)Max. Lift (Ft. (meter) H 2.10 BACK PRESSURE SPRING INSTALLATION
2 O) mRoy ARA1010 (3)mRoy HRH1010 (3)mRoy PRP1010 (3)mRoy BRS105 (1.5)RM105 (1.5)RB102 (.6) 13 Flush and blow out all pipelines before connecting thepump. This eliminates any foreign matter that mightseriously damage the internal working parts of the liq-uid end. Install a 20 mesh Y-type strainer that is sizedto remove foreign particles with minimum pressuredrop in the suction line of the pump.Install shut-off valves, with unions on the pump side ofthe valves, in the suction and discharge lines to facili-tate servicing.Use extreme care in piping to plastic liquid end pumpswith rigid pipe such as PVC. If excessive stresses or vibration is unavoidable, flexible connections are rec-ommended.