MOYNO® 500 PUMPS - 300 SERIES MOTORIZED - SERVICE MANUAL - DESIGN FEATURES - INSTALLATION - OPERATION - TROUBLESHOOTING

Oct 25, 2026

Service manual for MOYNO® 500 motorized pumps, covering 300 series models 331, 332, 333, and 344. Specifies construction materials (cast iron/316 SS housing, chrome-plated AISI 416 or 316 rotor/stator components, NBR/EPDM/FPM elastomers) and mechanical seal details. Provides installation guidance (mounting orientation, pre-wetting, piping support, electrical wiring and voltage tolerance), operating rules (self-priming limits, dry-run prohibition, lubrication flow requirement, rotation direction), and safety cautions. Includes pump data tables for ports, voltage ratings, discharge pressures, and temperature limits, plus troubleshooting steps for failure to pump, overloads, noisy operation, seal leakage, and priming issues.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages5

Reading Time13 min

AccessFree to download

DESIGN FEATURES

Housing and components

INSTALLATION

Mounting position

Pre-wetting and piping

Electrical connections

OPERATION

Self-priming and dry-run warning

Pressure and temperature limits

TROUBLESHOOTING

Failure to pump

Pump overloads

Noisy operation

Seal leakage

Pump will not prime

PUMP DISASSEMBLY

Disassembly safety and steps

Section: MOYNO® 500 PUMPS Page: 1 of 4 Date: March 1, 1998 SERVICE MANUAL MOYNO® 500 PUMPS 300 SERIES MOTORIZED 331, 332, 333, AND 344 MODELS DESIGN FEATURES Housing: Cast iron/316 SS Pump Rotor: Chrome plated AISI 416 stainless steel/Chrome plated 316 stainless steel Pump Stator: NBR (Nitrile) Seal: Mechanical (carbon/ceramic) Motor Shaft: AISI 416 stainless steel/ANSI 316 stainless steel Motor: 1/2 HP, 60 Hertz, 1725 rpm, totally enclosed, fan cooled (TEFC) C-Faced, 1 phase 115/230Vor 3 phase 230/460V (other motor options available; consult sales representative) Note: Alternate elastomers available. Refer to Repair/Conversion kit numbers pages 3 and 4. INSTALLATION Mounting Position. Pump may be mounted in any position. When mounting vertically, it is necessary to keep bearings above seals to prevent possible seal leakage into bearings. Pre-Wetting. Prior to connecting pump, wet pump elements and mechanical seal by adding fluid to be pumped into suction and discharge ports. Turn pump over several times in a clockwise direction to work fluid into pump elements. Piping. Piping to pump should be self-supporting to avoid excessive strain on pump housings. See Table 1 for suction and discharge port sizes of each pump model. Use pipe“dope” or tape to facilitate disassembly and to provide seal on pipe connections. Electrical. Follow the wiring diagram on the motor nameplate or inside the terminal box for the proper connections. The wiring should be direct and conform to local electrical codes. Check power connections for proper voltage. Voltage variations must not exceed ±10% of nameplate voltage. Motor is provided with internal automatic overload protection. To prevent damage to pump, pump rotation must be clockwise when facing pump from motor end. OPERATION Self-Priming. With wetted pumping elements, the pump is capable of 25 feet of suction lift with pipe size equal to port size. Be sure suction lines are air tight or pump will not self prime. Self-priming capabilities will vary due to fluid viscosity. DO NOT RUN DRY. Unit depends on liquid pumped for lubrication. For proper lubrication, flow rate should be at least 10% of rated capacity. Pressure and Temperature Limits. See Table 1 for maximum discharge pressure of each model. Unit is suitable for service at temperatures shown in Table 2. Storage. Always drain pump for extended storage periods by removing bottom drain plug in pump body. Caution: Suction pressure should never be greater than discharge pressure. Table 1. Pump Data | Pump
Model | Suction
Port
(NPT) | Discharge
Port
(NPT) | Voltage
Rating
(VAC) | Discharge
Pressure
(psig) | | --- | --- | --- | --- | --- | | 331 | 3/4 | 3/4 | See Motor Name
Plate For
Voltage Ratings | 150 | | 332 | 3/4 | 3/4 | See Motor Name
Plate For
Voltage Ratings | 100 | | 333 | 3/4 | 3/4 | See Motor Name
Plate For
Voltage Ratings | 50 | | 344 | 3/4 | 3/4 | See Motor Name
Plate For
Voltage Ratings | †30 | †With 3/4 HP motor, pressure is 40 psig. Table 2. Temperature Limits | Elastomer | Temperature Limits | | --- | --- | | *NBR | 10°-160°F | | *EPDM | 10°-210°F | | *FPM | 10°-240°F | *NBR = Nitrile EPDM = Ethylene-Propylene-Diene Terpolymer FPM = Fluoroelastomer Page 2 TROUBLESHOOTING WARNING: Before making adjustments, disconnect power source and thoroughly bleed pressure from system prior todisassembly. Failure to do so could lead to electric shock or serious bodily harm. Failure To Pump. 1. Motor will not start: Check power supply. Voltage must be ± 10% of nameplate rating when motor is in locked rotor condition. Check for faulty capacitor on 1 phase Models. 2. Motor runs and thermally kicks out: Check for excessive discharge pressure. Check for defective centrifugal switch on 1 phase Models. Increase ventilation to motor. Do not use less than \#14 wire size. 3. Stator torn; possible excessive pressure: Replace stator, ch

FAQs

What electrical voltage tolerance must be maintained for MOYNO® 500 pumps?

Voltage variations must not exceed ±10% of the motor nameplate voltage. The troubleshooting section also notes voltage requirements in locked rotor conditions (±10% of nameplate rating).

How does the pump achieve self-priming and what limits apply?

With wetted pumping elements, the pump self-primes with up to 25 feet of suction lift when pipe size matches the port size. Suction lines must be air tight; self-priming varies with fluid viscosity.

What should be checked if the motor starts but the unit thermally trips?

Check for excessive discharge pressure and, for 1-phase models, a defective centrifugal switch. Increase motor ventilation and ensure wiring uses no less than #14 wire size.

Oct 25, 2026

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