<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2024 Workiva-->
<!--r:7a822a55-5a37-448b-9dee-19d926240bc5,g:2b7a7b35-c459-4917-9045-c9e10739117d-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:spxc="http://www.spx.com/20240403" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2022-03-31" xmlns:dtr-types1="http://www.xbrl.org/dtr/type/2020-01-21" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.spx.com/20240403">
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2022-03-31" schemaLocation="https://www.xbrl.org/dtr/type/2022-03-31/types.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei-sub/2023" schemaLocation="https://xbrl.sec.gov/dei/2023/dei-sub-2023.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/ecd-sub/2023" schemaLocation="https://xbrl.sec.gov/ecd/2023/ecd-sub-2023.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="spxc-20240403_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="spxc-20240403_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="spxc-20240403_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="spxc_AdditionsForPriorServiceCostMember" abstract="true" name="AdditionsForPriorServiceCostMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_GrantDateFairValueOfStockAwardsMember" abstract="true" name="GrantDateFairValueOfStockAwardsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_DifferenceInFairValuesBetweenPriorYearEndFairValuesAndVestDateFairValuesForAwardsGrantedInPriorYearsMember" abstract="true" name="DifferenceInFairValuesBetweenPriorYearEndFairValuesAndVestDateFairValuesForAwardsGrantedInPriorYearsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_TotalAdjustmentsForPensionMember" abstract="true" name="TotalAdjustmentsForPensionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="spxc_YearEndFairValueOfAwardsGrantedInTheYearMember" abstract="true" name="YearEndFairValueOfAwardsGrantedInTheYearMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_FairValuesAtVestDateForAwardsGrantedAndVestedInCurrentYearMember" abstract="true" name="FairValuesAtVestDateForAwardsGrantedAndVestedInCurrentYearMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_DividendsOrDividendEquivalentsNotIncludedTotalCompensationMember" abstract="true" name="DividendsOrDividendEquivalentsNotIncludedTotalCompensationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_AdjustmentToCompensationAmountEquityAwards" abstract="false" name="AdjustmentToCompensationAmountEquityAwards" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="spxc_AdjustmentForSummaryCompensationTablePensionMember" abstract="true" name="AdjustmentForSummaryCompensationTablePensionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_TotalAdjustmentsForEquityAwardsMember" abstract="true" name="TotalAdjustmentsForEquityAwardsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_ForfeituresDuringCurrentYearEqualToPriorYearEndFairValueMember" abstract="true" name="ForfeituresDuringCurrentYearEqualToPriorYearEndFairValueMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_IncreaseDeductionInFairValuesForUnvestedAwardsGrantedInPriorYearsMember" abstract="true" name="IncreaseDeductionInFairValuesForUnvestedAwardsGrantedInPriorYearsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="spxc_AdditionsForCurrentYearServiceCostMember" abstract="true" name="AdditionsForCurrentYearServiceCostMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
</xs:schema>
