Grundfos · Submersible Well Pump
77S SP
77 GPM class stainless steel submersible well pump for 4 in and larger wells: 32 complete builds from 3/4 to 10 HP on Grundfos 4 in and 6 in motors, with a 2 in NPT discharge.
77 GPM Rated Flow
3/4-10 HP
37-396 ft Nominal Head
2 in NPT Discharge
4 in Min. Well · 6 in on 6 in Motors
230V 1Ph · 230V and 460V 3Ph
AISI 304 Stainless Steel
4.0-5.5 in Dia x 27.0-99.0 in L
26.7-136.4 lb Weight
Overview
The Grundfos 77S is the 77 GPM class of the Grundfos SP 4 in submersible range: a multistage pump end in AISI 304 stainless steel, factory-assembled on a Grundfos 4 in or 6 in submersible motor and sold as one complete pump. The 10 models run from 3/4 to 10 HP, single-phase 3-wire and three-phase, for household and farm wells, irrigation and light commercial supply.
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Stainless steel hydraulics. Standard S-series impellers and chambers are AISI 304 stainless steel, supported by stainless external components.
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Sand-handling bearing design. Water-lubricated bearings and sand channels reduce abrasive wear in suitable well-water service.
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Built-in check valve. Helps prevent backflow after shutdown and reduces the risk of water hammer.
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Upthrust control. A stop ring limits axial movement of the shaft during startup.
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Protected inlet and cable routing. The inlet strainer limits larger-particle entry, while the screw-mounted cable guard secures the motor lead along the pump.
What Ships and What It Needs to Run
Included: the 77S pump end and its Grundfos motor, factory-assembled as one complete pump.
Single-phase 3-wire builds: control box required, ordered separately. Use the Grundfos SA-SPM6 3-Wire Control Box matched to the motor horsepower; the box for each HP is in the Control Box by Horsepower table under Models & Performance. The 3/4 HP box is sold in packs of ten.
Three-phase builds: magnetic starter or drive required, ordered separately. Wire the motor through a starter or a drive (VFD) rated for its horsepower and voltage.
Drop cable and splice kit: sized to your setting depth and ordered separately.
Genuine Grundfos equipment, factory-new in original packaging — sold and supported by Watermain Supply, an independent industrial supplier.
Warranty
24 months from date of installation, but not more than 30 months from date of manufacture. In Grundfos's words, products are “warranted to the original user only to be free of defects in material and workmanship”; the full terms are in the installation and operating instructions on the Data Sheet tab.
Specifications
| Specification |
Value |
| Rated flow |
77 GPM nominal; actual flow depends on the selected model and system head |
| Horsepower |
3/4 to 10 HP |
| Supply options |
230V 1Ph; 230V 3Ph; 460V 3Ph |
| Motor diameter |
4 in or 6 in, depending on the complete-pump part number |
| Motor families |
MS402, MS4000C, MS6000C; configuration depends on selected assembly |
| Discharge |
2 in NPT |
| Well diameter |
Assemblies with 4-inch motors fit 4-inch and larger wells; 6-inch motor selections require a 6-inch minimum well. |
| Maximum sand content |
150 ppm for SP 35S-77S |
| Minimum pump submergence |
5 ft below pumping water level, subject to installation requirements and adequate motor cooling |
| Curve tolerance |
ISO 9906 Annex A |
| Included |
Pump end and motor, assembled as one complete pump |
Source: Grundfos SP data booklet and SP 77S data sheet, 60 Hz.
Models & Performance — Will It Do What You Need?
Each table reads like the curve: the head the pump adds at shut-off, along its curve and at the rated flow of 77 GPM, out to the end of the published curve. Pick a model whose head at your flow covers the pumping level, the pressure you need at the surface (2.31 ft per psi) and pipe friction.
| Model |
HP |
0 GPM (Shut-off) |
19.1 GPM |
48 GPM |
77 GPM (Rated) |
95.6 GPM (Max) |
| 77S07-2 |
3/4 |
56 |
52 |
45 |
37-38 |
20 |
| 77S15-3 |
1-1/2 |
85 |
80 |
71 |
61 |
35 |
| 77S20-4 |
2 |
113 |
108 |
95 |
77 |
49 |
| 77S30-6 |
3 |
170 |
163 |
145 |
113-117 |
78 |
| 77S50-8 |
5 |
230 |
220 |
197 |
157-159 |
111 |
| 77S50-10 |
5 |
285 |
273 |
243 |
192-195 |
136 |
| 77S75-12 |
7-1/2 |
346 |
333 |
299 |
237-240 |
174 |
| 77S75-15 |
7-1/2 |
430 |
414 |
371 |
293-297 |
213 |
| 77S100-17 |
10 |
490 |
471 |
423 |
337-340 |
246 |
| 77S100-20 |
10 |
572 |
551 |
493 |
392-396 |
284 |
Total head in feet. The shut-off and flow columns are read from the Grundfos 60 Hz curves, digitized from the published vector curves in the Grundfos SP 77S data sheet (60 Hz), at the nearest published point and rounded down. The (Rated) column is the nominal head Grundfos prints for each model at its rated flow, verbatim; where two figures are shown, builds on different motors or voltages differ slightly. 1 ft of head = 0.433 PSI. Full curves are in the product images and on the Data Sheet tab.
Control Box by Horsepower (single-phase 3-wire builds)
| Motor HP |
Volts |
Models |
Standard control box |
| 3/4 HP |
230V |
77S07-2 |
98821632 (10-pack) |
| 1-1/2 HP |
230V |
77S15-3 |
98315254 |
| 2 HP |
230V |
77S20-4 |
98315256 |
| 3 HP |
230V |
77S30-6 |
98315258 |
| 5 HP |
230V |
77S50-8, 77S50-10 |
98315260 |
Grundfos US price list, January 2026, p. 48. Every box, Standard and Deluxe, is on our Grundfos SA-SPM6 3-Wire Control Box listing. Three-phase builds need a magnetic starter or drive instead.
What It Delivers on a 30/50 Pressure Switch
Output at 30 and 50 PSI · 3 HP · 1 model · depths 20 to 50 ft
GPM at 30 PSI (switch cut-in), by depth to water
| Model |
20 ft |
30 ft |
40 ft |
50 ft |
| 77S30-6 |
90.5 |
85.5 |
80 |
73 |
GPM at 50 PSI (switch cut-out), by depth to water
| Model |
20 ft |
30 ft |
40 ft |
50 ft |
| 77S30-6 |
58.5 |
46.5 |
32 |
15 |
Output at 30 and 50 PSI · 5 to 10 HP · 6 models · depths 50 to 450 ft
GPM at 30 PSI (switch cut-in), by depth to water
| Model |
50 ft |
100 ft |
150 ft |
200 ft |
325 ft |
450 ft |
| 77S50-8 |
92.5 |
70 |
22 |
— |
— |
— |
| 77S50-10 |
— |
86 |
64.5 |
24.5 |
— |
— |
| 77S75-12 |
— |
— |
84 |
65.5 |
— |
— |
| 77S75-15 |
— |
— |
94.5 |
84 |
34 |
— |
| 77S100-17 |
— |
— |
— |
91.5 |
60.5 |
— |
| 77S100-20 |
— |
— |
— |
— |
77 |
36.5 |
GPM at 50 PSI (switch cut-out), by depth to water
| Model |
50 ft |
100 ft |
150 ft |
200 ft |
325 ft |
450 ft |
| 77S50-8 |
72 |
26 |
— |
— |
— |
— |
| 77S50-10 |
87 |
66.5 |
27.5 |
— |
— |
— |
| 77S75-12 |
— |
85 |
67 |
35.5 |
— |
— |
| 77S75-15 |
— |
95 |
85 |
71.5 |
— |
— |
| 77S100-17 |
— |
— |
92 |
82.5 |
38 |
— |
| 77S100-20 |
— |
— |
— |
91 |
66 |
10 |
Calculated, not printed: Grundfos publishes no output table for the SP 77S. Each cell is the flow where the published 60 Hz curve meets the depth to water plus 69 ft (30 PSI) or 116 ft (50 PSI), interpolated between published points and rounded down to 0.5 GPM. 77S07-2, 77S15-3, 77S20-4 cannot hold 50 PSI from a 20 ft depth on the published curve and are left out. Riser and pipe friction are not included. A dash on the shallow side means the flow runs past the end of the published curve; on the deep side, the pump cannot reach that pressure (or gives under 1 GPM).
Before You Buy — The Limits That Decide the Fit
| Check |
What to confirm |
| Well size |
Assemblies with 4-inch motors fit 4-inch and larger wells; 6-inch motor selections require a 6-inch minimum well. |
| Submergence |
At least 5 ft of water above the pump at the pumping level |
| Single phase |
3-wire builds need the Grundfos control box for the motor HP, ordered separately |
| Three phase |
A magnetic starter or drive rated for the motor, ordered separately |
| Cooling and temperature |
Water up to 104°F with at least 0.25 ft/s flowing past a 4 in motor (0.50 ft/s on a 6 in MS6000); drinking water up to 86°F |
| Sand |
150 ppm for SP 35S-77S |
Materials of Construction
| Part |
Material |
| Impellers and chambers |
AISI 304 stainless steel |
| Valve casing and suction interconnector |
Cast stainless steel, EN 1.4308 (standard S construction) |
| Strainer, straps and cable guard |
AISI 304 stainless steel |
| Pump shaft |
Stainless steel, EN 1.4057 |
| Bearings |
LSR/FKM elastomer |
| Neck rings |
TPU/PPS-FKM |
| Motor |
Water-filled Grundfos submersible motor; materials and seal design depend on motor type |
Source: Grundfos SP data booklet, standard S construction.
For engineering-led sizing and selection support or a factory submittal, email sales@watermainsupply.com or call 1-888.510.4036.
© Watermain Supply — A division of E4 Industrial LLC
