2 pipe steam vac question

lostinheating

Hi I was wondering if someone can help. I'm super of 75 unit building and having a problem in 1 unit of steam banging but only at night.  
    The vac system is fairly new approx 3 years  old. It makes strong vac on the upper floors but hits the vac pump cut off of 10". Vac dies down kicks back on. If I run the vac system with no heat will it still make vacuum and hit the limit?
  

EBEBRATT-Ed

Yes if the system is tight it should make vacuum even when not steaming. I think that's what your question was.

lostinheating

Yes thank you..

Pumpguy

Just FYI, returning condensate temperature is directly related to vacuum pump performance. The colder the condensate temperature the vacuum pump sees, the greater is its efficiency. And the opposite goes for high temperature condensate.

Just be sure your vacuum pump always has water in the tank. It's water usage, in one form or another that produces the vacuum.

EBEBRATT-Ed

@lostinheating

And if you have any bad steam traps fix them. Traps blowing steam and condensate that is too hot will kill a vacuum pump

lostinheating

All new traps my main problem is the vac system builds vac faily quickly and cuts out on high vac 10". I was wondering if that's causing noise issues.  Pitching the Coils is out of question so to speak.  And the complaint only comes at night.

EBEBRATT-Ed

@Pumpguy
would know more than I but I think most vacuum systems run about 5-7" of vacuum. What steam pressure are you running at. I would keep it as low as possible.

Are you able to locate where the noise comes from?

Even new trap parts can sometimes be bad. Do you have TRVs on the radiation?

lostinheating

Boiler runs to 5 max psi. Even on low fire all time noise was still heard. What are trvs? 
    No I have not located it. I've tested during day system running,system cold I did not hear anything. Even set boiler to come on under 55 day or night. Still same.
   Vac pump hits the limit every time.

Pumpguy

EBEBRATT-Ed said:

@Pumpguy
would know more than I but I think most vacuum systems run about 5-7" of vacuum. What steam pressure are you running at. I would keep it as low as possible.

Are you able to locate where the noise comes from?

Even new trap parts can sometimes be bad. Do you have TRVs on the radiation?

Usual vacuum switch settings are OFF @ 8" Hg. and ON when vacuum drops back to 3" Hg. This maintains an average system vacuum of 5.5" Hg.

Square D is the usual brand of switch used these days. Their switches can be ordered pre-set to the 8 and 3 settings.

For Duplex vacuum pump installations there usually 2 vacuum switches. The high set set switch would be wired through an electronic alternator and is the LEAD switch. This alternate starts the vacuum pumps with each cycle.

The LAG vacuum switch would also be set to shut off @ 8" Hg. and close when the vacuum drops to 2" Hg. The LAG switch would be wired to either turn on the opposite vacuum pump, or both together, depending on the control circuit logic.

In either case, the LAG vacuum switch brings in both vacuum pumps under peak load conditions. It also provides start - stop operation when only one vacuum pump is operational.

EBEBRATT-Ed

@lostinheating
Most old buildings were designed to run 2psi or less. Sometimes the pressure is raised to keep the burner from short cycling.

What you could try is lower the pressure to cut the burner off at 1 1/2psi. Maybe that will eliminate or reduce the hammering. If it does maybe your tech can down fire the boiler a little