What is the recommended pressure for this expansion tank?

They come pressurized from the manufacturer with a required 4-6 psi.

What is the size of the male threaded fitting on the top? 3/8"?

Size? Mine is in storage so not sure . The thread is tapered for a tight fit. Check APEC web site. It likely is the 3/8". Appears to be less than 1/2" and for sure more than 1/4"

What is the recommended pressure for this expansion tank?

Label on my tank says 100 psi max. At one point, my tank was not putting out much water. I hooked up a pump which said there was about 20psi in the tank. I charged it to 95 and it works like it did when it was new.

I need replacement tank for my Ecowater ero335. Is this a comparable model. The company here says everything out there is plastic.

I do t know if this will fit your exact model. But it should. just make sure the intake/outtake valve is the same size as your current tank. This one is definitely not plastic and the water has tasted great.

Systems Tank-4 4 Gallon Residential Pre-Pressurized Reverse Osmosis Water Storage Tank

Product ID: 256163481

Details

Brand
APEC WATER
Capacity
4 gallons
Material
Stainless
Product dimensions
27.9L x 27.9W
Special features
Heavy Duty

💧4 gal pre-pressurized capacity

🔄vertical/horizontal discharge

🛡️food-grade, certified bladder

₨8516

Duties & taxes included

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Details

Brand
APEC WATER
Capacity
4 gallons
Material
Stainless

Description

💧 Elevate your hydration game with the RO tank that keeps pace with your lifestyle!

PREMIUM SAFETY DURABILITY - Food-grade bladder and CE-certified materials ensure leak-proof, odor-free water storage you can trust.
SEAMLESS SYSTEM INTEGRATION - 1/4 inch male pipe thread inlet/outlet designed specifically for reverse osmosis systems for effortless connectivity.
CONSISTENT HYDRATION NO WAIT - Pre-pressurized 4-gallon tank delivers up to 3.2 gallons of purified water instantly, perfect for busy households.
FLEXIBLE INSTALLATION ZERO HASSLE - Engineered for both vertical and horizontal placement with included tank stand—fits seamlessly into any under-sink setup.
TRUSTED BY THOUSANDS RATED 4 6 ⭐ - Join over 2,400 satisfied users who upgraded their water quality and flow with this industry-standard tank.

The APEC Water Systems Tank-4 is a 4-gallon pre-pressurized reverse osmosis water storage tank designed for residential use. It efficiently holds up to 3.2 gallons of purified water and supports both vertical and horizontal installation. Constructed with a food-grade bladder and certified materials, it guarantees safe, odor-free, and leak-proof water storage. Featuring stainless steel connectors and a 1/4 inch male pipe thread inlet/outlet, it integrates seamlessly with most RO systems. Highly rated by thousands, this durable tank is ideal for average to large families seeking reliable, high-volume purified water on demand.

Specifications

Asin	B00LU28SHE
Best Sellers Rank	#195 in Under-Sink Water Filters
Date First Available	20 April 2015
Is Discontinued By Manufacturer	No
Item Model Number	TANK-4
Manufacturer	APEC Water Systems
Product Dimensions	27.94 x 27.94 x 36.83 cm; 900 g

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