Open pipe and high water pressure

[Mel_n_Chibi]

Hi, I'm a new homeowner and have a few plumbing problems. I've searched the forum and cannot find answers to two problems (there are so many more, but I am limiting this to the two biggest problems):

1. Open pipe in the basement. It is attached to the main line under the basement floor that goes out to the sewer. The basement does have a funny smell, but it is not overwhelming at the moment.
What do I do about this pipe?

About the house, it was built in 1930. The pipe in question is cast iron and looks like it was cut. The previous owners moved the sink when they remodeled and it looks like they just cut the old cast iron pipe from the old sink. I can only assume it was the drain for said sink. The previous owner also did all of his own work from the looks of it, and did not do a good job.

The pictures in order are the old sink, the pipe and the pipe in relation to other fixtures.


2. My water pressure is 100 psi. This was tested in the evening when all of my neighbors were home. There is a pressure regulator at the meter in the house, but it looks like it is really old.

I'm currently replacing some of the copper with PEX and installing a new water heater. Checking the water pressure was so I could figure out what size expansion tank to get for the water heater.


I've tried getting plumbers out to look at them, but have had 4 no-call no-shows.

 

[Reach4]

1. I am thinking a flex cap or "test plug".

2. That old WATTS PRV looks like it is ready to be replaced. If that were 3/4, you could add a Sharkbite slip PRV in series with the old PRV as a temporary action, until you could get it done pretty.

 

[Sponsor]

 

[Tuttles Revenge]

Definately plug the open drain and vent pipes. They're allowing sewer gases into your home.

The Pressure Reducing Valve PRV can easily be replaced or potentially serviced. It might even be working but out of adjustment.

These are not the instructions for that particular model.. but they're mostly the same and will be mostly relevant.
http://media.wattswater.com/1910259.pdf

 

[Mel_n_Chibi]

Many thanks!! I'll probably get the sharkbite as a stop gap so I can get a properly sized expansion tank.

According to my internet searches, I need a 3.2 gallon expansion tank for an 80 gallon water heater at 50-60 psi. Does that sound correct?

 

[Tuttles Revenge]

Here is a chart. You have 3 variables. Incoming pressure and size of tank as you know.. but stored water temperature is the 3rd.

https://www.amtrol.com/resources-rewards/selection-tools/#thermal-tank-form

or this odd chart that doesn't take 120° hot water into consideration.

https://www.amtrol.com/wp-content/uploads/2020/09/MC8520-06_20-TXT-Sizing-Chart.pdf

 

[Fitter30]

45* entering, 120* out 80 gallons of water = 4.2 gallons of expansion
https://www.engineeringtoolbox.com/volumetric-temperature-expansion-d_315.html