Spence PRV sizing criteria

MarkWest

Looking for resource material relating to the origin of the 3:1 specific volume rule described in the Spence PRV sizing criteria. It can be found in the Spence Designer's Guides, specifically on page 112 of the 3rd edition.
Any help is appreciated!

EBEBRATT-Ed

You would have to ask Mr Spence. I am sure other manufacturers follow the same or similar requirements.

I just read the first section on single stage regulators. So they want you to fulfill 3 criteria.

PRV will control to only 1 pressure
Turndown cannot exceed 10:1 That means lbs of steam at high load must not exceed the low load lbs of steam by a ratio that exceeds 10-1 so 10lb of steam at low load 100lbs of steam at max load for example would be max turndown

However, steam volume cannot be greater than 3:1

Example 100 psi inlet and 5 psi outlet. 100lb steam has a volume of 3.89lb/cubic foot. 5 lb steam has a volume of 20.1lb/cubic feet.

20.1/3.89= a ratio of 5.16 so reducing from 100-5 is NG according to what I figured with 1 regulator

jumper

In this age steam to steam generator is worth the extra expense. It lessens steam quality issues.

RPK

Jumper, besides steam quality, what are the advantages of using a steam/steam generator vs a PRV?

Intplm.

I have found Spence PRV's to be problematic unless delt with directly with the manufacturer. Try them for your most accurate info. 1-800-398-2493

EBEBRATT-Ed

I only had a problem with Spence valve once. Had 3 of them I installed and 1 was fine. The other two the outlet pressure wouldn't stay steady. They would creep and creep just slightly.

Always seemed to be a pilot problem. Took them apart, could not find a problem reassembled them and they worked

Intplm.

EBEBRATT-Ed said:

I only had a problem with Spence valve once. Had 3 of them I installed and 1 was fine. The other two the outlet pressure wouldn't stay steady. They would creep and creep just slightly.

Always seemed to be a pilot problem. Took them apart, could not find a problem reassembled them and they worked

Same problem I had @EBEBRATT-Ed, but the problem did not go away. After much adjustment, I had to make the phone call.

jumper

RPK said:

Jumper, besides steam quality, what are the advantages of using a steam/steam generator vs a PRV?

Another advantage is that condensate returning to fired high pressure boiler can be at higher pressure. Also tends to be cleaner and doesn't have to be reconditioned for feedwater.

Thermostatic feed forward control MIGHT require less service than pressure controlled PRV. I emphasize might because with industrial service instruments one never knows.

Occasionally you see steam/steam in district heating when all condensate is dumped; so somebody bought it.

jumper

>> Also tends to be cleaner and doesn't have to be reconditioned for feedwater.

Paradoxically situation was other way around in industrial facilities with steam bled from turbines. Then it was the low pressure system steam that had no turbine oil issues.