Flojet 21010-003 Diaphragm Kit EPDM/Poly for Duplex Series Pumps
When a Flojet duplex diaphragm pump starts losing pressure, cycling erratically, or leaking past the head, the diaphragm is usually the part that wore out first — not the motor. The 21010-003 kit is the fix. It pairs an EPDM elastomer diaphragm with polypropylene pistons, the same combination the pump left the factory with, so the rebuilt pump goes back to its original stroke volume and pressure cut-out instead of limping along at reduced output.
EPDM is the reason this particular version exists. It handles hot water, glycol solutions, dilute acids and alkalis, and a wide range of agricultural chemicals far better than Buna or Viton would, which is why it shows up in ag spraying rigs, beverage and post-mix dispensing, industrial washdown carts, water treatment skids, RV and mobile water systems, and plenty of general-purpose transfer work. EPDM is not the right choice for petroleum-based oils and fuels — if that is what the pump is moving, a Viton or Buna kit is the better match.
Replacing the diaphragm is a straightforward bench job on the 2100 and 2130 platform: pull the six head screws, lift the upper housing and valve assembly, swap the diaphragm and pistons together, and torque everything back down. Always fit the new pistons that come with the kit rather than reusing the old ones, and orient the raised side of the diaphragm toward the motor. Most technicians replace the check valve set at the same time, since both wear from the same fluid and the same hours. Keeping a kit on the shelf turns an unplanned pump failure into a twenty-minute repair instead of a new pump purchase.
Key Features
- Genuine Flojet service part, part number 21010-003
- EPDM diaphragm paired with polypropylene pistons
- Restores original flow rate, pressure cut-out, and priming ability
- Broad chemical compatibility with water, hot water, glycol, dilute acids, dilute alkalis, and many agricultural chemicals
- Supports the duplex design's ability to run dry intermittently without damage
- Pistons supplied with the diaphragm so the wear pair is replaced as a matched set
- Bench-serviceable with basic hand tools, no special press or fixture required
- Extends pump service life and avoids full pump replacement
Applications
- Agricultural and horticultural spray rigs, boom sprayers, and spot sprayers
- Chemical metering, dosing, and transfer systems
- Beverage dispensing, post-mix, and syrup delivery equipment
- Water treatment and filtration skids
- Industrial and commercial washdown carts
- Car wash and pressure cleaning support systems
- RV, mobile, and off-grid potable water systems
- Livestock watering and pasture spraying equipment
- Marine freshwater and deck wash systems
- General-purpose light-duty liquid transfer
Specifications
- Part number: 21010-003
- Product type: Diaphragm repair kit
- Diaphragm material: EPDM
- Piston material: Polypropylene
- Configuration: Duplex, two-piston
- Brand: Flojet, a Xylem brand
- Compatible pump families: Flojet 2100 Series and 2130 Series duplex diaphragm pumps
- Representative pump models: 2130-132, 2130-232
- Related service parts: check valve kit 20028-053 EPDM, cam bearing 21004-302, pressure switch 02090-115
- Recommended fluid temperature: up to approximately 130°F / 54°C
- Not recommended for: petroleum oils, fuels, and solvents incompatible with EPDM
- Sold as: one complete diaphragm kit
Frequently Asked Questions
Q: How do I know whether my pump needs a diaphragm kit or a check valve kit?
A: Weak or falling pressure with the motor running normally usually points to the diaphragm. A pump that will not hold pressure and short-cycles when no outlet is open, or one that will not self-prime, usually points to the check valves. When a pump has years of service on it, replacing both at once is the more reliable repair.
Q: Why choose the EPDM version instead of the Viton or Buna version of this kit?
A: EPDM is selected for hot water, glycol, dilute acids and alkalis, and many agricultural chemicals. Viton is chosen for aggressive solvents and certain harsh chemicals, and Buna for petroleum-based fluids. Matching the elastomer to the fluid is the single biggest factor in how long the diaphragm lasts.
Q: Do I have to replace the pistons that come in the kit?
A: Yes. The pistons and diaphragm wear as a pair, and reusing worn pistons against a new diaphragm causes uneven loading and premature failure. Install both together, with the radiused corner of each piston facing the diaphragm.
Q: Can the pump still run dry after the diaphragm is replaced?
A: The duplex design tolerates intermittent dry running, and a correctly installed new diaphragm restores that tolerance. Extended dry running still generates heat and shortens diaphragm life, so it should be treated as a safety margin rather than a normal operating mode.
Q: How often should this kit be replaced in routine maintenance?
A: There is no fixed interval, since service life depends on fluid, temperature, duty cycle, and how often the pump runs against a closed outlet. Operators running chemicals or hot fluids daily often schedule a rebuild annually, while light seasonal use can go several years between kits.
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