GP500520 is the earlier Kohler number for the Rite-Temp pressure balancing unit, and GP800820 is the current one. The unit sits in the brass body behind the mixer cap in K-304, K-305 and K-11748 valves. It has no stem of its own.
Schematic of the Kohler unit as Kohler describes it, not to scale. It shows only the features named on this page. No bench photo of this part yet.
Specifications
OEM numbers
GP500520 (earlier), GP800820 (current, Kohler says it replaces GP500520)
Kohler's names
Pressure balancing unit (PBU); Cartridge in the 2011 service parts catalog; Rite-Temp cartridge in the service parts brochure; regulator on a service kit sheet
Type
Pressure balancing unit for single-handle tub and shower valves. A separate piece behind the mixer cap
Valves
Kohler Rite-Temp K-304, K-305 and K-11748, 1/2 in. pressure-balancing
The earlier pressure balancing unit alone, no cap. Kohler's 2011 catalog lists it as the cartridge beside the GP77759 cap for K-304, K-305 and K-11748.
GP800820
Kohler
The current number for the unit alone. Kohler's service parts brochure lists it as the Rite-Temp cartridge for most 1/2 in. pressure-balancing valves and says it replaces GP500520.
GP77759
Kohler
The mixer cap alone, no unit. Kohler calls it the stem cap. It is the companion part, not a number this unit replaces.
GP876851
Kohler
Kohler's kit of GP800820 plus GP77759. Cap and unit together, so a different order from the unit alone.
Where it goes
Kohler's 2011 service parts catalog lists GP500520 as the cartridge, with the GP77759 cap, for the K-304 Rite-Temp 1/2 in. pressure-balancing valve, and the same pair for the K-11748 and K-305 valves with diverter.
Kohler's valve identification tool names Mixer Cap and PBU as the common service parts for the K-304, the K-305 and the K-11748.
Kohler's brochure lists GP800820 as the cartridge for most 1/2 in. pressure-balancing valves and says it replaces GP500520.
Kohler's 3/4 in. high-flow valves and the K-8304 are listed with different cartridges.
Confirm it is your part
With the trim already off, look at the stem first. A round stem under a black plastic cap held by two screws leads to Kohler's K-304, K-305 or K-11748 answers. A square stem is a Coralais branch, not covered.
Count the screws that hold the cap to the valve body. Two: K-304, K-305 or K-11748. Four: K-8304, which takes a one-piece cartridge. Six: K-306 or K-2971 Hi-Flow, which takes a different unit.
Look for a diverter button. None is a K-304. A button with no threads on its end is a K-305. A threaded button is a K-11748. Kohler lists the same GP500520 and GP77759 for all three.
The unit is a separate piece inside the brass body, behind the mixer cap. It has no stem of its own.
A metal collar sits over the front of the cap, under the two screws. Kohler notes it is sometimes not present. The collar is not part of the unit.
Kohler's K-304 instructions describe a notch cut into the back of the unit and small O-rings on the back. Kohler's PBU page calls the O-ring location oval-shaped. On an old unit already out, look for the notch.
A brass cap with a three-ribbed stem is an early valve. Kohler Assist says a new unit there needs the GP876851 cap and unit combination, so the unit alone is not the order.
Look-alikes
Kohler GP800820, the current number
Why it gets confusedKohler lists it as the number that replaces GP500520, so the two numbers get used for the same job.
How to tellSame position, same valves. Kohler's brochure says GP800820 replaces GP500520. No opened document describes a visible difference between the two.
Kohler GP876851 or GP76851, cap and unit kit
Why it gets confusedThe unit is half of that kit, and Kohler's brochure calls the kit a pressure-balancing cartridge and mixer cap kit.
How to tellThe kit includes the black mixer cap with its stem. This part is only the unit left in the body after the cap comes off.
Kohler GP77759, the mixer cap alone
Why it gets confusedIt is the cap that sits over this unit in the same valves.
How to tellGP77759 is the stem cap. It carries the stem. The unit has no stem, and Kohler lists the cap and the unit under separate numbers.
Kohler GP800881, cartridge for the K-8304
Why it gets confusedKohler lists it as a pressure-balancing cartridge under a number that reads almost the same as GP800820.
How to tellKohler calls it a one-piece pressure-balancing cartridge for the K-8304 valve. That cap is held by four screws. Valves for this unit have two.
Kohler GP1144925 and the 85500 cap
Why it gets confusedSame layout on Kohler's Hi-Flow Rite-Temp valve: a cap over a pressure balancing unit.
How to tellKohler's catalog lists them for the 3/4 in. K-306 and K-2971 valves. Its identification tool sends a six-screw cap to those valves, not a two-screw cap.
Cross-reference numbers
Numbers other makers and sellers list against this part. The notes say how far each one goes.
Maker
Number
Note
Kissler
46-0080
pressure balancing unit only; one retailer page
Not printed on this page
Where the sources disagree, the figure is left off until it is settled.
Length, diameter and any other size of the unit. Sources disagree, so no figure is printed.
Material and color of the unit. No Kohler document states either, so neither is printed.
GP800881. Kohler lists it as a one-piece cartridge for the K-8304, a different part, so it is not shown here as a match.
Sterling fitment and the Sterling number some retailers print. Only retailer pages make the link. No Kohler or Sterling document was found.
Coralais valves and store-brand numbers. Kohler lists 500520 in Coralais parts sheets, but that fit is not claimed here. No opened page ties other store numbers to this unit.
FourHome replacement
The FourHome replacement for Kohler GP500520 ships as one pressure balancing unit per pack, without a mixer cap.
FourHome replacement
Replacement for Kohler GP500520 Rite-Temp Pressure Balance Unit
Catalogs disagree now and then, and makers revise parts without changing the number. Compare the old part before buying. Identify by measurement lists every indexed part near a given length and spline count.
