Should 1040-V payment voucher check be sent with the tax papers, or separetly ?

It can be sent with the tax return. Do not attach the voucher or check to the tax return. Make sure you get some sort of mail confirmation from your postal carrier. 

Per IRS; Do not use staples or paper clips to affix your payment to your voucher or return.

• Make sure your check or money order includes the following information:
  • Your name and address
  • Daytime phone number
  • Social Security number (the SSN shown first if it's a joint return) or employer identification number
  • Tax year
  • Related tax form or notice number

I found these instructions on investopedia.com, hope this helps! I did try to include the link bur for some reason it said it was not correct although it would still take me to correct website.  So I just copied and pasted the results.  Good Luck!!

"How to File Form 1040-V: Payment Voucher

The payment voucher at the bottom of Form 1040-V should be detached and mailed with your tax return and payment. The voucher asks for four main pieces of information.

• Line 1: Your Social Security number (SSN)
• Line 2: The SSN of your spouse, if you’re filing a joint return
• Line 3: The amount you are paying via check or money order
• Line 4: Your name and the street address that is shown on your tax return3
   

The IRS does not accept cash payments by mail. You must send a check or money order to cover the amount of your annual tax bill. They should be made payable to "United States Treasury." To avoid any problems processing your payment, make sure your name and address appear on the check or money order.4 You should also include a daytime phone number and your SSN on the payment. If filing a joint return, write the SSN listed first on your Form 1040, 1040-SR, or 1040-NR."