⚙️ Waterway Viper 56 Spa Pump 3721621-1V — 4.0 HP 2-Speed 230V

High-volume performance engineered for swim spas and large-scale installations

📋 Product Overview

The Waterway Viper 56 (Part No. 3721621-1V) is a high-performance, 4.0 HP dual-speed jet pump designed, engineered, and manufactured in the USA by Waterway Plastics of Oxnard, California. Unlike the Executive series with its 6-1/2″ wet end, the Viper features a massive 8″ diameter wet end specifically engineered to move higher volumes of water at lower pressures — making it the ideal choice for swim spas, large multi-jet spas, and other high-flow applications.

Built on the robust 56-frame motor platform, the Viper delivers powerful output at 3,450 RPM on high speed and energy-efficient circulation at 1,725 RPM on low speed. The extra-large 2-1/2″ intake and discharge ports provide significantly improved flow performance and reduced noise compared to standard 2″ connections. The pump features Waterway’s premium Viton shaft seal with silicone carbide faces and 316 stainless steel casing for exceptional chemical resistance. The wet end rotates 90 degrees for flexible installation positioning. This model also ships under the updated Waterway designation MV-40226-25.

✨ Key Features

✅ 4.0 HP Dual-Speed Motor — Full-rated 56-frame motor delivers 3,450 RPM on high speed for powerful jets and 1,725 RPM on low speed for quiet filtration

✅ 8″ Diameter Viper Wet End — Oversized wet end specifically designed for 56-frame motors, engineered to move higher volumes of water at lower pressures than the Executive series

✅ Extra-Large 2-1/2″ Intake & Discharge — Larger ports provide significantly improved flow performance, higher volume throughput, and reduced operational noise

✅ Swim Spa Optimized — Purpose-built for high-volume, low-pressure systems where maximum water movement is critical

✅ 56-Frame Construction — Larger motor frame provides added strength, cooler operating temperature, and longer motor life than 48-frame pumps

✅ Viton Shaft Seal — Silicone carbide faces with 316 stainless steel casing and Viton bellows deliver exceptional corrosion resistance against chlorine, bromine, and salt water systems

✅ Two Double-Shielded Ball Bearings — Moisture-resistant grease packing delivers quieter operation and longer bearing life

✅ Split Capacitor Design — Separate start and run capacitors reduce energy consumption during operation

✅ Thermal Overload Protection — Built-in motor protection automatically shuts down the pump if overheating is detected, extending motor life

✅ 90-Degree Rotatable Wet End — Versatile discharge positioning for flexible installation in any spa cabinet configuration

✅ Four Insulated Winding Sets — Dual-speed motor features four sets of insulated windings for increased efficiency

✅ UL and CUL Certified — Third-party safety certified for the US and Canadian markets

🔧 Technical Specifications

Specification	Value
Pump Type	Jet Pump (Dual-Speed)
Series	Viper 56
Primary Part Number	3721621-1V
Updated Part Number	MV-40226-25
Model Code	PV-40-2N22C
Manufacturer	Waterway Plastics (Oxnard, CA, USA)
Motor Power	4.0 HP (Full Rated)
Speed Settings	Dual Speed (2-Speed)
High Speed RPM	3,450 RPM
Low Speed RPM	1,725 RPM
Voltage	230V
Frequency	60 Hz
Phase	Single Phase
High Speed Amperage	12.0 A
Low Speed Amperage	4.4 A
Frame Type	56Y Frame (Thru-Bolt)
Wet End Diameter	8″
Discharge Port	2-1/2″ MBT (Male Buttress Thread)
Suction Port	2-1/2″ MBT (Male Buttress Thread)
Union Thread OD	3-5/8″ (approximately 3.6″)
Discharge Position	Side Discharge
Suction Position	Center Suction
Seal Type	Viton — Silicone Carbide, 316SS Casing
Seal Kit Part Number	319-3010B
Bearings	Two Double-Shielded Ball Bearings (Moisture-Resistant Grease)
Capacitor	Split (Start and Run)
Thermal Protection	Yes — Automatic Overload
Wet End Rotation	Every 90 degrees
Unions Included	No — sold separately
Power Cord Included	No — sold separately
Certifications	UL Listed, CUL Listed
Warranty	1 Year Manufacturer Warranty

⚠️ Important — Viper vs Executive: The Viper uses 2-1/2″ connections (3-5/8″ OD across threads). If your current pump has 2″ connections (3-1/16″ OD across threads), you need the Executive model 3721621-1D instead.

⚡ Electrical Requirements

Electrical Spec	Requirement
Supply Voltage	230V
Frequency	60 Hz
Phase	Single Phase
Full Load Amps (High Speed)	12.0 A
Full Load Amps (Low Speed)	4.4 A

⚠️ IMPORTANT ELECTRICAL SAFETY NOTICES:

All electrical work must be performed by a licensed electrician in accordance with the National Electrical Code (NEC) and all applicable local building codes.

Hot tubs and spas require GFCI (Ground Fault Circuit Interrupter) protection — this is mandated by the NEC for all spa and hot tub installations.

A dedicated circuit is required — do not share the circuit with other appliances.

Make sure the wiring voltage matches the motor voltage (230V). Connecting to incorrect voltage will damage the motor and void the warranty.

Ground the motor prior to connecting electrical power. Do not ground to a gas supply line.

For 2-speed models: Do NOT wire both speeds to run simultaneously.

The pump cord and plug are intended to be used with a mating spa pack connector. Refer to the wiring diagram on the motor nameplate or terminal cover for proper connections.

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🔗 Compatibility Guide

Frame & Wet End Configuration:

📍 Frame: 56Y Frame (Thru-Bolt mounting) 📍 Wet End Diameter: 8″ (Viper series) 📍 Discharge: 2-1/2″ MBT — Side discharge 📍 Suction: 2-1/2″ MBT — Center suction 📍 Union Thread OD: 3-5/8″ across pump threads

Important Compatibility Notes:

There is no industry standard for pump unions — various brands have their own unique thread style and size. You must use unions compatible with this pump’s 2-1/2″ Male Buttress Thread connections. If your existing pump uses different unions, you may need to cut off your old unions and install new ones. If your heater is directly coupled to the wet end, this pump may not be compatible due to different union threading.

Do NOT over-power your spa by upgrading from a 48-frame motor to a 56-frame motor without verifying compatibility with your spa’s plumbing and control system.

Can Replace the Following Pump Models:

Aqua-Flo XP3 (08330002-5041) — the Viper wet end is a direct replacement for the XP3 series

Substitutes Available:

Aqua-Flo XP3 (08330002-5041) and LX 56WUA400A-II can be used as substitutes for this pump

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🛠️ Installation Requirements

Mounting:

Requirement	Specification
Mounting Position	Horizontal — must be installed below water level (flooded suction)
Base	Solid, level surface with adequate floor drainage
Location	Installation area must be clear of direct water and have adequate drainage
Moisture Protection	Pump should be protected from excessive moisture

Plumbing:

Connection	Specification
Suction (Intake)	2-1/2″ Male Buttress Thread — Center
Discharge (Outlet)	2-1/2″ Male Buttress Thread — Side
Union Type	Waterway tailpiece assemblies recommended (sold separately)
Union Tightening	HAND TIGHTEN ONLY — do NOT use a wrench or adhesives
Sealant	Use only Teflon tape — do NOT use pipe dope or chemical sealants (causes stress cracking of plastic parts)
Pressure Test	Must not exceed 40 PSI; ensure all air is removed from the system

Installation Notes:

⚠️ Pump must be installed below water level to ensure flooded suction — never allow the pump to run dry

⚠️ Install shut-off valves on both inlet and outlet for future maintenance

⚠️ Never run pump dry — causes immediate seal damage and voids warranty

⚠️ Ensure proper grounding and bonding per NEC requirements

⚠️ GFCI protection is required by code for all hot tub and spa installations

⚠️ The wet end can be rotated every 90 degrees by loosening the four motor thru-bolts and turning the pump head to the desired discharge position

⚠️ When replacing an existing pump, mark your wires for “common,” “high speed,” and “low speed” before disconnecting

⚠️ Do NOT install this Viper wet end on a 48-frame motor — it is designed exclusively for 56-frame motors

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🔄 Maintenance Guide

Routine Maintenance:

Task	Frequency	Notes
Check for leaks	Monthly	Inspect around shaft seal and union connections
Inspect unions	Monthly	Hand tighten if needed — never use a wrench
Clean strainer/filter	As needed	Remove debris to maintain proper flow
Check amperage draw	Annually	Should be within 10% of nameplate rating (12.0A high / 4.4A low)
Inspect motor vents	Quarterly	Keep clear of debris for proper cooling
Check mounting bolts	Quarterly	Tighten if vibration has loosened them
Verify drain plug	Quarterly	Ensure no leakage from drain port

Warning Signs — Replace Pump If:

• Unusual noise (grinding, screeching, or loud humming)
• Water leaking from the shaft seal area
• Motor repeatedly trips the circuit breaker
• Noticeably reduced water flow or weak jets
• Motor overheating or hot to the touch
• Pump hums but will not start (capacitor or winding failure)
• Visible corrosion on the motor housing

Seal Replacement:

📍 Seal Type: Viton — Silicone Carbide, 316SS Casing 📍 Seal Kit Part Number: 319-3010B 📍 Wet End Volute: 315-1500 📍 Volute Faceplate: 311-1510 📍 Impeller (4.0 HP): 310-2200 📍 Wear Ring: 313-3210 📍 Volute O-Ring: 805-0264 ⚠️ The Viper uses a different seal (319-3010B) than the Executive series (319-3100B / BSP-1000) — do NOT use Executive seals on a Viper wet end ⚠️ Replace seal at the first sign of leakage to prevent motor damage

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🎯 Ideal Applications

Application	Suitability	Notes
♨️ Swim spa jet pump	Yes	Primary application — 8″ wet end moves high volumes for swim current and jets
♨️ Large hot tub jet pump	Yes	Ideal for large multi-jet spas requiring maximum water volume
♨️ High-flow spa systems	Yes	2-1/2″ ports and oversized wet end optimize flow in high-volume configurations
🛁 Standard hot tub (2″ plumbing)	No	Requires 2-1/2″ plumbing — use Executive 3721621-1D for 2″ connections

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❓ Frequently Asked Questions

Q: What is the difference between the Viper and the Executive? A: The Viper has a larger 8″ diameter wet end (vs 6-1/2″ on the Executive) and uses 2-1/2″ connections (vs 2″ on the Executive). The Viper is designed for high-volume, low-pressure applications like swim spas, while the Executive is optimized for higher head pressure in standard hot tubs. They share the same motor but have different wet ends.

Q: What horsepower is this pump? A: This pump is full-rated at 4.0 HP. It is a dual-speed motor operating at 3,450 RPM on high speed and 1,725 RPM on low speed.

Q: Will this fit my hot tub? A: This pump uses a 56Y frame with an 8″ Viper wet end and 2-1/2″ Male Buttress Thread connections (3-5/8″ OD across threads) on both suction and discharge. If your current pump has 2″ connections (3″ OD across threads), you need the Executive model 3721621-1D instead.

Q: What voltage does this pump require? A: 230V / 60Hz single phase. All electrical installation must be performed by a licensed electrician in accordance with the NEC and local codes.

Q: Is this a single or dual speed pump? A: Dual speed (2-speed). High speed runs at 3,450 RPM for jet operation, and low speed runs at 1,725 RPM for quiet filtration. This pump can also be wired for single-speed operation if needed.

Q: What size are the ports? A: Both suction and discharge are 2-1/2″ Male Buttress Thread (MBT). The outside thread diameter measures approximately 3-5/8″ (about 3.6 inches). The suction is center-mounted and the discharge is side-mounted.

Q: Does this pump come with unions? A: No, unions and power cord are sold separately. Waterway tailpiece assemblies are recommended for best connection. Compatible 2-1/2″ unions are available on Parts4Tubs.

Q: What warranty is included? A: Waterway provides a 1-year manufacturer warranty covering defects in materials and workmanship. Contact Parts4Tubs for full warranty terms.

Q: Can I use this pump to replace an Aqua-Flo XP3? A: Yes, the Waterway Viper is a verified replacement for the Aqua-Flo XP3 (08330002-5041). Match the amperage rating and connection sizes to ensure proper compatibility.

Q: How do I know if my pump needs replacing? A: Common signs include unusual noise (grinding or screeching), water leaking from the seal area, reduced jet power, the motor tripping the circuit breaker, the pump humming but not starting, or the motor running excessively hot.

Q: Do I need a GFCI breaker? A: Yes, GFCI protection is required by the National Electrical Code (NEC) for all hot tub and spa installations in the United States.

Q: What is the updated part number for this pump? A: This pump also ships under the updated Waterway designation MV-40226-25. Both part numbers refer to the same pump.

Q: Can I use Executive seals on this pump? A: No. The Viper uses a different seal kit (319-3010B) than the Executive series (319-3100B / BSP-1000). Using the wrong seal will cause leaks and pump failure.

📥 Downloads & Resources

📄 Installation Manual — 48/56 Frame Executive, EX2, & Viper Pumps (810-0061.1111) — Official Waterway installation instructions, wiring guide, troubleshooting, and exploded parts diagram

🏆 Why Choose the Waterway Viper 56 (3721621-1V)

✅ Maximum Water Volume — The 8″ diameter Viper wet end moves significantly more water than the 6-1/2″ Executive, making it ideal for swim spas and high-flow applications

✅ USA Designed & Manufactured — Engineered and built in Oxnard, California by Waterway Plastics, with over 50 years of industry experience

✅ 56-Frame Advantage — Larger motor frame runs cooler and lasts longer than 48-frame designs, providing added strength and durability

✅ Viton Seal with Silicone Carbide — Premium chemical-resistant shaft seal with 316SS casing stands up to aggressive sanitizers including chlorine, bromine, and salt systems

✅ Quiet Operation — Extra-large 2-1/2″ ports reduce intake noise, while double-shielded ball bearings with moisture-resistant grease minimize mechanical noise

✅ Energy-Efficient Dual Speed — Low speed provides quiet, efficient filtration while high speed delivers full jet power on demand — split capacitor design further reduces energy consumption

✅ UL and CUL Certified — Third-party safety tested and listed for peace of mind

✅ Proven Aqua-Flo XP3 Replacement — Verified direct replacement for the Aqua-Flo XP3 series, with the same connection sizes and comparable performance

🔄 Alternate Part Numbers & Cross-References

This pump is sold under, replaces, or is cross-referenced with the following part numbers:

3721621-1V, MV-40226-25, 3721621-0V, PV-40-2N22C, PV-40-2N22M, PV-30-2N22M, PV-30-2N22C, WW37216211V, 37216211V, 1-00-0106, 5175-304, 15-350-1621, 7-187563-02, 34-270-3508, 34-270-3508N, 34-270-3508W, 3721621-1T, 37216211T, 3721621-0T, 3721621-0T06, 3721621-0T5A, 3721621-0T7E, 3721621-0T7H, 3721621-0T8C, 3721621-0V5A, 3721621-0V72, 3721621-0V86, 3721621-1T7E, 3721621-1T85, 3721621-1T86, 3721621-1V5AU, 3721621-1V6N, 3721621-1VHZN, 3711621-0T (1-Speed), 3711621-0T7N (1-Speed), 5KCP49UN9096XVIPER, 0-187563-02, R63MWENA-4727 (motor), Aqua-Flo XP3 08330002-5041

🤝 Why Buy from Parts4Tubs

✅ US-based support for American customers

✅ Fast shipping across the United States

✅ Expert advice from spa and hot tub specialists

✅ Competitive pricing in USD

✅ Full warranty support

✅ Hassle-free returns

✅ Replacement seals, wet ends, impellers, and parts available

✅ Compatible 2-1/2″ unions and AMP cords available to order with your pump

Need Help? Contact our team for compatibility advice — we can help verify whether you need the Viper (2-1/2″ connections) or Executive (2″ connections) and confirm the correct union size and voltage for your installation.

💫 Summary

The Waterway Viper 56 (3721621-1V) is a USA-made, 4.0 HP full-rated dual-speed jet pump featuring an oversized 8″ diameter Viper wet end and extra-large 2-1/2″ connections specifically engineered for swim spas and high-volume applications. Operating at 230V/60Hz with 12.0A high speed and 4.4A low speed draws, this UL/CUL-certified pump delivers maximum water volume at lower pressures with quiet, reliable performance. The premium Viton shaft seal with silicone carbide faces and 316SS casing ensures long-term chemical resistance. Backed by Waterway’s manufacturer warranty, order today from Parts4Tubs for fast US shipping and expert compatibility support.

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	Magic Plastics Union 0602-15 (1.5″ Pump Union) | 1-1/2″S x 1-1/2″FBT Union, Pump, Magic, 1-1/2"S x 1-1/2"FBT (Industry Standard) w/ O-Ring	$6.36 Max: 575 Min: 1 Step: 1 Add to cart
	Magic Plastics Union 0602-20 (2″ Pump Union) | 2″S x 2″FBT w/ O-Ring Union, Pump, Magic, 2"S x 2"FBT (Industry Standard) w/ O-Ring	$8.00 Max: 491 Min: 1 Step: 1 Add to cart
	Waterway Union 400-6010 | 2-1/2″ Union Nut with 2-1/2″ Slip tailpiece and o-ring (2.5″ union) Union, Pump, Waterway, 2-1/2"FBT x 2-1/2"S	$14.77 Max: 145 Min: 1 Step: 1 Add to cart
	1 Speed Pump / Blower / AMP Cord | 21086 Amp Plug, Pump, 1-Speed, 14/3, 4-Pin, 5' Cord, White	$24.71 Max: 426 Min: 1 Step: 1 Add to cart
	Balboa Amp Plug 21087 (For 2 Speed Pumps) Amp Plug, Pump 1 (2-Speed) 14/4, 72" Long, White	$31.72 Max: 176 Min: 1 Step: 1 Add to cart

Hot Tub Pump Collar & Union Size Chart

Imperial & Metric Specifications

Union Size	Collar Size	Thread OD	Union OD	O-Ring Size
1.5" Female Buttress Thread (FBT)	2.5" / 64mm (Tip to Tip) Measurement	2-1/2" 64mm	2-13/16" 71mm	2-5/16" OD 59mm
2" Female Buttress Thread (FBT)	3.1" / 78mm (Tip to Tip) Measurement	3-1/16" 78mm	3-3/8" 81mm	2-15/16" OD 75mm
2.5" Female Buttress Thread (FBT)	3.6" / 91mm (Tip to Tip) Measurement	3-5/8" 91mm	4-1/4" 108mm	3-7/16" OD 87mm

Important Notes

The union "size" (1.5", 2", 2.5") is nominal and doesn't correspond to any actual measurement.

Collar size is measured from thread tip to thread tip on the pump outlet.

Most hot tub pumps use Female Buttress Thread (FBT) - 98% of applications.

O-ring gaskets may vary between manufacturers - measure your existing gasket for accuracy.

How do I Replace a Hot Tub Pump?

Here's a general step-by-step guide on how to replace a hot tub pump. Keep in mind that the specific steps may vary depending on your hot tub's make and model, so it's essential to consult your hot tub's manual for model-specific instructions. If you're not comfortable with this procedure, it's a good idea to seek professional assistance.

Materials You'll Need:

• Replacement pump
• Pipe wrench
• Adjustable wrench
• Screwdriver
• Pipe sealant (thread tape or plumber's putty)
• PVC primer and cement (if you have PVC plumbing)
• Teflon tape (for threaded connections)

Procedure:

1. Turn Off the Power: Before you begin, ensure the hot tub's power supply is turned off at the circuit breaker or disconnect switch. Safety should always be a priority when working with electrical components.

2. Drain the Hot Tub: If your hot tub is not already empty, you'll need to drain it. Follow your hot tub's manual or manufacturer's instructions for proper draining. (You might not need to do this if you can lock the pump off with the gate valves)

3. Locate the Pump: Identify the location of the existing pump in your hot tub. It's usually located near the equipment area or in a designated pump compartment.

4. Disconnect the Electrical Wiring: Carefully disconnect the electrical wiring from the old pump. This typically involves removing the electrical conduit cover, unscrewing wire nuts, and disconnecting the wires from the terminals. Be sure to note the wire connections or take a picture for reference when connecting the new pump.

5. Disconnect the Plumbing: Depending on your hot tub's plumbing setup, you'll need to disconnect the plumbing connections to the pump. Use a pipe wrench or adjustable wrench to loosen and remove the fittings. Be prepared for some water spillage when disconnecting the plumbing.

6. Remove the Old Pump: Once the electrical and plumbing connections are detached, carefully remove the old pump from its mounting position. Some pumps may be secured with mounting brackets or bolts.

7. Prepare the New Pump: If the new pump is not pre-assembled, you may need to attach fittings, unions, or adapters to match your hot tub's plumbing. Ensure that you use the appropriate sealant or Teflon tape on threaded connections to prevent leaks.

8. Mount the New Pump: Position the new pump in the same location as the old one and secure it in place using the mounting brackets or bolts.

9. Reconnect Plumbing: Reconnect the plumbing to the new pump, ensuring that all connections are tight and secure. If your hot tub uses PVC plumbing, use PVC primer and cement to bond the connections properly.

10. Reconnect Electrical Wiring: Reconnect the electrical wiring to the new pump, following the notes or pictures you took earlier. Make sure all wires are properly connected and secure.

11. Turn On the Power: Restore power to the hot tub by switching on the circuit breaker or reconnecting the disconnect switch.

12. Test the Pump: Turn on the hot tub's pump to ensure that it's working correctly. Check for any signs of leaks or irregularities in the plumbing connections.

13. Refill the Hot Tub: Once you've confirmed that the new pump is functioning properly, refill the hot tub with water.

14. Check for Leaks: Inspect the plumbing connections for any leaks. If you find any, turn off the pump, drain the tub again, and reseal the connections as needed.

15. Monitor: Keep an eye on the pump and plumbing for the next few days to ensure everything is functioning correctly and that there are no further issues.

Remember that this is a general guideline, and the specific steps may vary based on your hot tub's design. If you're unsure or uncomfortable with any aspect of this process, please do get in touch, happy to help.

How do I know what size hot tub pump I have?

Determining the size of your hot tub pump is an important step when it comes to maintenance or replacement. To find out the size of your hot tub pump, follow these steps:

1. Check the Manual: The easiest way to determine the size of your hot tub pump is to consult the owner's manual or user documentation that came with your hot tub. The manual typically contains detailed information about the specifications and components of your hot tub, including the pump.

2. Look at the Pump Housing: If you don't have access to the manual or it doesn't provide the information you need, inspect the pump itself. Most hot tub pumps have a label or plate on the pump housing that displays essential details, including the pump's model number, manufacturer, and specifications. You can then send that to me or Google it.

3. Measure the Pump: If the label is missing or damaged, you can measure the pump's dimensions. Measure the diameter of the pump's wet end (the part where the water flows) and the length of the wet end. These measurements can help identify the size and capacity of the pump.

4. Consult the Manufacturer: If you can't find the information on the pump or in the manual, contact the hot tub manufacturer or a reputable dealer. Provide them with your hot tub's model and serial number, and they should be able to identify the correct pump size for your specific hot tub.

5. Online Research: You can also search online using the pump's model number or hot tub's make and model. Many manufacturers provide detailed information about their products on their websites, and you may find specifications for your pump model.

Once you have determined the size and specifications of your hot tub pump, you can proceed with maintenance, repairs, or replacement if necessary. Keep in mind that replacing a hot tub pump with the same size and capacity as the original is crucial to ensure proper water circulation and filtration in your hot tub. If you're unsure about any aspect of this process, get in touch, always happy to help.