can this relief valve be used to drain water from the air tank

Its' purpose is to relieve pressure - that's what it's designed for.I would not use it to drain water from a tank; it would likely corrode the components and compromise its' effectiveness.You will never find one of these on a compressor at the bottom of the tank - there's a drain there; it's always placed toward the top away from water build up.

Does it release right at 200psi because I have a 200psi pressure switch.

If working properly the safety will blow at 200, if the safety valve psi is lower than the pressure switch set point it will blow before it reaches the set point, so the comp will never shut off, the safety valve should be about 30 lbs more than the pressure switch set point. A 200 psi safety switch is common on a comp set to 165-175 psi.

What is the maximum negative temp that this valve will work with? For example -20c?

I would not trust a $5 relief value without checking with the manufacture first.

if you want to reduce pressure mechanically through the relief valve , do you have to unthread the valve or is there a special action for that?

No, you don't unthread the valve body. You just have to pull on the key ring. A spring keeps the valve closed; at the pressure the valve is rated for, the air pressure overcomes the spring force and allows the valve to open and relieve pressure. Pulling on the key ring hard enough allows you to overcome the spring force and open the valve; when you release the key ring, the spring should immediately close the valve.

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Description

🔒 Secure Your Safety with Style!

SAFETY FIRST - ASME safety rated with UV and NB marks, ensuring peace of mind in high-pressure scenarios.
UNMATCHED DURABILITY - Crafted from premium brass and stainless steel for ultimate corrosion resistance.
HIGH PERFORMANCE FLOW - Achieve a powerful flow rate of 178 cfm, ensuring efficiency in every application.
PRECISION ENGINEERING - Set pressure precisely at 200 psi, designed for reliability in critical environments.
VERSATILE COMPATIBILITY - 1/4" male NPT inlet connection fits seamlessly into various systems.

The Control Devices ST25-1A200 ST Series Brass ASME Safety Valve is engineered for high-performance applications, featuring a preset relief pressure of 200 psi and a robust flow rate of 178 cfm. Constructed from durable brass with a stainless steel spring, this valve is designed to withstand temperatures up to 250°F, making it ideal for demanding environments. With its 1/4" male NPT threaded inlet, it offers versatile compatibility and is ASME safety rated, ensuring reliability and safety in every use.

Specifications

Material	Brass
Brand	Control Devices
Item Dimensions LxWxH	5 x 1 x 1 inches
Exterior Finish	Stainless Steel,Zinc
Inlet Connection Size	0.25 Inches
Inlet Connection Type	National Pipe Tapered
Outlet Connection Type	MNPT
Outlet Connection Size	0.25 Inches
Valve Type	safety valve
Manufacturer	Control Devices
Part Number	ST25-1A200
Item Weight	1.13 ounces
Product Dimensions	5 x 1 x 1 inches
Country of Origin	USA
Item model number	ST25-1A200
Size	0.25 Inch
Style	Threaded
Item Package Quantity	1
Flow Rate	178 Cubic Feet Per Minute
Measurement System	Inch
Included Components	Safety Valve
Batteries Required?	No
National Stock Number	4820-01-621-8959

Reviews

B**

Big Steve

It works great

19.02.2025

J**Z

psi

Good quality

21.05.2025

T**T

Easy installation.

I bought this pressure relief valve to replace the one in my new compressor.I had changed one of the female fittings and broke the manifold. I broke the pressure relief valve trying the change it out. Worked like a charm once the new one was in.No problems.

8.02.2024

N**Z

Entrega genial

Exelente entrega anticipada y muy buen producto lo pude calibrar muy bien

16.03.2025

A**9

Good value, but sticks occasionally

I bought this to replace the original valve on my husky air compressor. The original valve's spring would not close the valve after letting go of the pull ring.This valve was about half the price of the factory replacement valve. So its price is it's biggest pro. It also is much smaller than the original valve, while having more scfm.One big con is that it can be sticky occasionally: It doesn't always close when you release the pull ring at high pressure (testing @175psi); it feels like that there is a bit of friction between its stem and bore; you have to nudge it a bit to get the spring to overcome this friction. Probably needs to be replaced, but I'm out of the return window. Also, while the sticking is annoying, it does not leak or open below its tested pressure; so I'll live with it for the time being.Another con is its pull ring. It's small and weak. I just replaced the pull ring with the one from the original valve of my compressor.

9.03.2021

J**N

👌

👍

13.12.2024

R**V

It worked like it was supposed to. Keeps me and my project safe.

20.08.2024

E**Y

works well so far

It has worked well for me, I have not tested the high end, but it hasn't lifted at 155

5.02.2024

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