[b]Set Pressure, CDTP and spring range .. Help please[/b]

[Bader]

Greeting Gentlemen,
I am kind of confused, Up to my knowledge the CDTP and set pressure should be within the manufacturer spring range. Now if this true where can I find this in standards. What's the purpose of the spring range!!?
Because some people say that it's not and some they say no it should be within the spring range and this is the purpose of the spring range to make sure that you are using the appropriate relief valves specification.
If it's true, would you please direct me where can I find this is it in the standards or manufacture recommendation manuals or where exactly?

I need to read more about this
Thanks for giving me your valuable time.

Regards,
Bader


I am always ready for help as much as i can .. so just let me know your Problem .

 

[bevjones2009]

hi mate, you are best off contacting the manufacturer and asking for them to supply any information you need.

 

[Chance17]

I searched my references and could not find a standard for "spring range".
Despite not having a standard, common sense indicates you must match the spring range to CDTP.

The CDTP is adjusted and set on the valve test stand.
The adjustment is made by turning a nut which compresses the spring.
You obiviously want a spring calibrated to operate within the desired CDTP.
You would not use a 5-50 spring if the CDTP is 200-psig.
The ideal target is to have a spring range somewhat mid-point to CDTP -- say 50-400 psi spring range if CDTP is 200-psig.

My references did note adjustment factors for temperature.
The spring set for 200-psig CDTP on the cold test stand will actiavate at a lower setting as the temperature increases.
Adjustment factors start at 250-F.

 

[Bader]

Many thanks..
All what you said is logically true, but as you sometimes others need excuse to escape from work

For this reason i was looking for standards and i found something in API520 para. 3.51

Many thanks again for your response

Regards

I am always ready for help as much as i can .. so just let me know your Problem .

 

[JAlton]

The answer to your inquiry is somewhat complicated because CDTP may compensate for Temperature or Back Pressure and in rare cases for both Temperature and Back Pressure.

If the CDTP is compensating for Increased Temperature, the Spring is selected based on Set Pressure not CDTP. This is because the spring will react properly to the increase in pressure in the protected system once the temperature has stabilized.

If the CDTP is compensating for Back Pressure, the Spring is selected based on the CDTP, not the nameplate Set Pressure because the Back Pressure is a real force on the disc the same as spring force. The Set pressure and CDTP do not both necessarily need to be within the same spring range.

In the rare case of temperature and back pressure the spring is chosen based on the CDTP for the same reason as simple back pressure above.

The purpose of the Spring Range is to match the Spring Rate to the force acting on the PRV Disc from the system pressure. Spring rate is based on Load X Deflection. The range of a spring is determined by the PRV Orifice because System Pressure X Area of Nozzle = Force exerted on the Disc. The spring needs to be strong enough to hold the PRV closed, but not so strong that the PRV cannot reach full lift and thereby flow the required capacity. However, it also needs to be strong enough to reclose the PRV within an acceptable pressure below set pressure, typically 90% to 93% of Set Pressure.

I hope this helps.




JAC